1) What’s the story behind the name you chose for yourself here?
Its the name of the battleship/fortress in Iain M. Banks novel ‘Use of Weapons’. The Mk2 bit had to be added because I made a mistake when signing up for the first time.
2) Do you use it everywhere?
No, just here.
3) If not, what other interesting aliases do you use online?
Thats a secret!
4a) Is your username gender neutral/confusing?
Don’t know, what gender do people assume I am from this nick?
It’s from my posting at the shakespeare.com bulletin board. You were allowed to choose a name each time you posted. One time, after a “Shakespeare didn’t write the plays” bit of nonsense, I wrote a post and was planning to use “Reality Check”; I accidentally typed my first name and it came out “RealityChuck.” I kept it.
Generally, if I use a nom de net, I use “RealityChuck,” though on some boards I used my real name.
N.A.
No one seems to.
1) What’s the story behind the name you chose for yourself here?
Rhiannon is an ancient Celtic goddess; 8404 is the number I tacked onto the end because “Rhiannon” was taken, it was my phone extension several jobs ago.
2) Do you use it everywhere? I use it almost everywhere
3) If not, what other interesting aliases do you use online? On parenting boards I am known as Charliesmom, which is pretty self-expanatory
4a) Is your username gender neutral/confusing? I would hope not, even those unfamiliar with the goddess herself should be aware of the Fleetwood Mac song.
4b) Has this ever caused you problems and/or entertainment? Nope.
1) What’s the story behind the name you chose for yourself here?
So, when I was a child, my name was Finn (it still is, as a matter of fact). People used to call me Finn-a-din-din, for reasons unknown (although I admit it is a pleasant alliteration). In some cases this was shortened to Din, and years later when I got a bit computer-literate, I used Din as my name on IRC. However, when it came time to get an email address, Din was taken, so it seemed obvious that what I should do is lengthen it to Dinaroozie (which wasn’t taken).
2) Do you use it everywhere?
Most places. In places where I can change my name a lot, like on MSN, I’m rarely Dinaroozie, but in places where the name is permanent, I am.
3) If not, what other interesting aliases do you use online?
I have variously been known as Arachnid Boy, Mr. Strong Tendons, and Child of Moon-Spinner. All of these have bizarre rationales behind them, but it’s probably best that I don’t go into that now.
4a) Is your username gender neutral/confusing?
I guess it could be. Occassionally people online will call me ‘Dina’ for short, which sounds a little feminine - I prefer ‘Din’ (see above).
4b) Has this ever caused you problems and/or entertainment?
Not really.
~ Isaac
1) What’s the story behind the name you chose for yourself here?
It was a private joke from another messageboard from which I’d taken a break (someone asked a friend who’d referred to me by name in a post who I was, and he replied that I was “an Internet Legend”). It’s decidedly tongue-in-cheek, especially given my general level of technological incompetence.
2) Do you use it everywhere?
I use it here and on one or two other boards, just for continuity.
3) If not, what other interesting aliases do you use online?
I used to use my full first and last names, until someone made a (probably not credible) threat against my children. I became much more leery of using real-life identifiers after that. I also use my Hotmail address in places I don’t frequent, and it’s a variant of “anonymous”.
4a) Is your username gender neutral/confusing?
Apparently it is.
4b) Has this ever caused you problems and/or entertainment?
I’ve never considered it a problem, and it’s never been particularly entertaining. On the other hand, Mr. Legend, who has a gender-neutral first name he uses on another board we both frequent, has often been mistaken for a woman, leading to hours of fun when people assumed we were a lesbian couple (not, as they would hasten to assure us, that there’s anything wrong with that).
1) What’s the story behind the name you chose for yourself here?
It comes from Bob Dylan’s great song Visions of Johanna.
2) Do you use it everywhere?
Yes, just about.
4a) Is your username gender neutral/confusing?
Au contraire, I chose it specifically as a feminine gender signal.
4b) Has this ever caused you problems and/or entertainment?
Problems? No. As for entertainment, I’ve worked up a pianistic arrangement of “Visions of Johanna” that I use as my theme song. As well as my other theme song, coincidentally from the same album: “Just Like A Woman” 
1. What’s the story behind the name you chose for yourself here?
Well, my parents found it in the New Age Baby Name book, lo, these many years ago. Seriously, when I had AOL my screen names were largely a variation of my name, and so I was addressed on the Dope by my real name. When this board came into being, I wanted people to know who I was.
2. Do you use it everywhere?
No. The handle I go by almost everywhere else is postmoderngirl. (Incidentally, I think postmodernism is bunk. I just happened to be studying it when I needed a handle.) I’ve thought abount changing my handle here, just because it’s confusing to people who are on both LJ and the SDMB that Kyla=postmoderngirl, but decided it’s even more confusing when people on the SDMB change their handles.
4a. Is your username gender neutral/confusing?
No.
4b) Has this ever caused you problems and/or entertainment?
No, but people do misspell my name a lot, despite the fact that it’s four letters long and presumably they could c&p.
**1) What’s the story behind the name you chose for yourself here? **
There were some powerpuff girls stickers on my desk when I was trying to think of a username and one said “Pokey Oakes Kindergarten” so I typed ‘pokey’. I didn’t expect I would ever post, I just wanted to search for something.
**2) Do you use it everywhere? **
Only here.
3) If not, what other interesting aliases do you use online?
Nothing interesting. I usually get inspiration by looking at something on my desk.
4a) Is your username gender neutral/confusing?
If I post anything sex related, people will think I like to poke things but I don’t because I’m female.
4b) Has this ever caused you problems and/or entertainment?
No.
I always imagined you look like Elvis Costello.
**1) What’s the story behind the name you chose for yourself here? **
Eh, I signed up around the time I was trying to stick to two usernames. Kendra was a slayer from Buffy the Vampire Slayer, and Ideals was just a last name of sorts I filled in. I don’t particularly like it, and am thinking of changing it before people start recognizing my sn.
**2) Do you use it everywhere? **
Nope. My most common is scarletswitchblade, but I find that one often brings connotations to peoples’ minds.
3) If not, what other interesting aliases do you use online?
Mostly scarletswitchblade, but other random ones where that wouldn’t fit. AThingWithFeathers is the one I’m thinking of changing to.
4a) Is your username gender neutral/confusing?
Not that I know of, but perhaps I don’t post enough for mistakes like that to happen.
4b) Has this ever caused you problems and/or entertainment?
n/a
I’ve read other “What’s the origin of your name?” threads, but this is by far the most thorough.
What’s the story behind the name you chose for yourself here?
I grew slowly. Very slowly, a “I was only 4’8” when I started high school" type of slowly. Because of this my childhood best friend decided when we were twelve or so I must be an elf…and by high school had tried to convince others of this too. Jokingly, I hope. This was one nickname that stuck.
Do you use it everywhere?
Nope.
If not, what other interesting aliases do you use online?
My stuff for The Sims and Sims 2 is The Evil Writer, and my fics everywhere and orginal fiction (just at fictionpress) are under Neoxphile; I use the names on message boards pertaining to the subjects as well.
4a) Is your username gender neutral/confusing?
You wouldn’t think that it would strike people as particularly masculine, but now and then someone assumes I’m male.
4b) Has this ever caused you problems and/or entertainment?
Once when I was a newbie on another board it was a bit of a problem, but it’s a boring story.
1) Ragiel is cited as author of the Book of Wings by every book on gemstone mythology or folklore I’ve yet read. He was either a medieval Arab scholar, or an angel sitting in seat 7, row 2, of the heavenly choir who may or may not have revealed the content of the book to the scholar. The passages quoted deal with the fantastic powers of particular stones once the proper images were engraved upon them. I’ve been collecting jewelry, gemstones, and legends about them for most of my life, and the title Book of Wings evokes the whole fascination of subject for me.
2) Pretty much everywhere. It’s uncommon. Googling it turns up several people with that surname, a reference or two to the angel, a mention of the author, and me.
3) None. I’ve tried out a couple, but they haven’t stuck.
4) The author would have been male, and angels traditionally don’t have gender, but the name seems to sound feminine to many people. I’m a woman, so that’s OK.
5) Nah.
1) What’s the story behind the name you chose for yourself here?
It’s my surname. No real story, it’s the name I prefer to go by.
2) Do you use it everywhere?
Not really no. I don’t like using my real surname on, what can only be considered, less mature (gaming) forums.
3) If not, what other interesting aliases do you use online?
I used to go by Achilles but Hollywood recently made that all too common. So I decided to put a tiny bit of effort into it and came up with Mak’shar Karrde, my main character name in most games, on most gaming forums. It’s a name derived from the two greatest characters in Star Wars lore, Admiral Akbar and Talon Karrde.
4a) Is your username gender neutral/confusing?
It only confuses stupid people.
4b) Has this ever caused you problems and/or entertainment?
If I never hear another Jinx/Jinks ‘joke’ again I’ll die a happy man.
So…do you hate meeses to pieces, then?
1) What’s the story behind the name you chose for yourself here?
Sophomore year of high school, we formed teams in PE for a baseball tournament. We had Giants, Yankees, Cubs, etc. And we had one team (not mine) who settled upon the name “Suburban Plankton”. The name just sort of stuck with me, but I never had occasion to use it until I came here 15 or so years later.
2) Do you use it everywhere?
I use it exclusively online now, except in cases where the maximum length for user names is less than 16 characters, in which case I just shorten it as required. Most other places I have eliminated the space and type it as just one word.
3) If not, what other interesting aliases do you use online?
This is it (see #2).
Sorry, I missed the last two questions on my first reading (my answers aren’t terribly interesting, but just for the sake of completion…).
4a) Is your username gender neutral/confusing?
I believe it’s gender neutral, but I’m not very knowledgeable on the sexual characteristics of plankton. I’m not even certain they *have *genders. And now I’m also not sure if “plankton” is singular, plural, or both.
Perhaps it is confusing after all.
4b) Has this ever caused you problems and/or entertainment?
Just a few quizzical looks when people have seen my email address, but nothing more.
silenus
*Related: Folklore
(sīlē´nes) , in Greek mythology, part bestial and part human creature of the forests and mountains. Part of Dionysus’ entourage, the sileni are usually represented as aged satyrs—drunken, jolly, bald, fat, bearded, and possessing horse ears. According to some myths they were prophets; but according to others they were so perpetually stupefied with drink that they were unable to distinguish truth from falsehood. In some legends only one such creature appears, Silenus, described as the oldest of the satyrs, the son of Hermes or Pan. He was the companion, adviser, or tutor of Dionysus. *
I don’t have the ears.
**1) What’s the story behind the name you chose for yourself here? **
it’s a misspelling of some kind of insult in Finland. There was a Finnish exchange student in my art history class when I was 16 and he taught me this one word in Finnish. I can’t even remember how you’re actually spell it (If anyone does, it would be greatly appreciated). But I used to go home and yell it at my sister as “Darrrrrrrrrrrrrrrrva!.” This was around the same time as I discovered straight dope. So I decided to shorten it and put the capitals in as a kind of mis-pronounciation guide.
**2) Do you use it everywhere? **
Nope, only here. I do occasionally yell it at people though.
4a) Is your username gender neutral/confusing?
I think it’s pretty neutral.
4b) Has this ever caused you problems and/or entertainment?
not as yet, but here’s hoping. . .
**1) What’s the story behind the name you chose for yourself here? **
It’s my initials and an old joke nickname from when I was a teenager. I’ll let you guess which part is which. 
**2) Do you use it everywhere? **
Pretty much just here and on irc when I’m in the #straightdope channel.
3) If not, what other interesting aliases do you use online?
This is pretty much the only non-work-related message board I post on. When posting on Usenet, I just use my name.
**4a) Is your username gender neutral/confusing? **
I don’t think so. I’ve always assumed it pretty obviously a guy kind of name, but who knows?
4b) Has this ever caused you problems and/or entertainment?
None that I’m aware of.
2&3. I don’t use it or (anything else) anywhere else because I don’t have a need for a nom de net anywhere else.
4b) Problems? Yes, once. I don’t mind correcting pronouns, but one time when I did so (“Just FYI, Eureka is a she”) one of the other posters went off on a really irritating riff about how I was just pretendingto be female. When said poster was banned not terribly long thereafter I did not miss him in the slightest.