ME!!
Online, I am tiggeril, a bouncy personage who duct tapes people to the walls while licking them and stuffing happy fuzzy bunnies down their pants and cooking gourmet meals and ordering strippers.
IRL? That’s me… on the couch, in the corner, by myself.
Hmmm… online, I can generally remain fairly well composed and clever. Jophiel, poster of knowledge in GQ and occassional chimer in in MPSIMS and the fair and rational leader of #SD.
IRL, I meet Dopers and awaken covered in make-up and with cryptic scribblings on my body in blue marker.
I think I just need to stay online 
No question about it.
I make a MUCH better impression IRL than online.
I can’t really think of anyone that hates me IRL.
Happy to report that Fierra was very well-behaved and by all appearances had a good time in A’dam, and that you, Una, were not forgotten. She’ll be back in the UK by the time you read this; otherwise you could just ring the hotel early morning CET (the number’s on the website). Oh, and don’t tell her I said this, but she’s a complete babe :D.
As for the OP, I can sum it up by saying I have good friends IRL, while online I suspect nobody knows me.
I think I make a much better impression online. I only have a couple of friends IRL. My closest friends live half the globe away, and I’ve never met them. I wouldn’t say that my online personality is better than my IRL one though, because they’re the same thing. But I’m more at ease online. IRL I’ve very shy with people I don’t know well and have self-confidence problems. I’m the one sitting just outside the group without saying much, pretending people care that I exist. With few exceptions, all people IRL I’ve ever called friends have made friends with me, not the other way around. It takes effort to crack my shell. I feel more at ease to be ‘me’ online, so it’s easier to get to know me (which is fairly often a prerequisite for friendship). With people I already know well I’m more like I am online (though this has yet to be tested by me actually meeting anyone I’ve made friends with on the net, ask me again in July :)).
I do have a few problems online as well though: I have something of a subtley sarcastic and self-mocking sense of humour, and many of the things I’m not sure if people can be certain whether or I’m being serious or not (this applies more in ICQ et al than on the boards). I try to make it clear with devices such as smilies (or grins, winks, etc), and this has led to my smilie(/etc) addiction, as I use them so much that I think people will think I AM serious if I don’t.
Hmm, I wandered a bit there. I’ll cease my ranmblings now.
I make an incredibly bad impression online AND IRL. Hey, there’s something to be said for consistency. Me, I have the consistency of cold oatmeal.
I think I come across as a bit of a bell-end online (at least, I do here). I think it’s because I’m not really relaxed about posting.
The same thing applies in real life until I feel at ease with people. I’d be imagining that that’s true for most people.
I dunno, I’m the same person in both modes, but RL conversation never unfolds quite like SDMB threads. I’m good at jumping in on the meat of the issue like happens here. I’m not so good at the niceties and small talk that grease the skids in the early hours or talking with someone IRL. The end result is that I seem a lot less lively in person. Sometimes I’m better than other times.
Perhaps not better, but definitely very diffrent from the picture people have of me offline.
IRL I am extrememly shy, so come across as abit mysterious and slightly snotty. I also keep forgetting to wear my glasses so have to squint at people to see what they look like - this is usually interpreted as a dirty look. I only get away with it coz I am small, pretty and cute.
Whereas online (well, in my few posts on SD anyway) I seem to be coming across as a screaming queen which would surprise my friends no end.
I am another one who makes a better impression IRL than OL. In real life, I am flirty and funny, whereas OL I come across as much more serious and much more boring, IMHO.
I need to work on those winky smilies.
I am much funnier, intelligent and engaging online, which is pretty sad, considering I’m none of those online. But I’m even less of them, IRL. I’d say I’ll be over on the couch with Tiggeril, except I blew off the last Chifest because I’m so shy around people I don’t know. EXCEPT I KNOW THEM! I met many of them at the last Chidope, and enjoyed their company and everything, but caught a case of the shys.
The only way I functioned in sales was by discovering my outgoing avatar, but a year and a half of working virtually alone killed him.
My ambition is to never have to actually see people IRL again . . . I can communicate through letters, E-mail, telephone, my books, author’s photos, the occasional TV or radio appearance. If I had the dough, I’d hire an “Eve” to go to dinners and teas and go outside to pick up my mail, so I could become a complete and perfect hermit.
Una,
Let me just say this.
I want to start a petition to meet you. really. Ask Fierra. I was practically begging her to bring you over to Dublin sometime so that we could meet you. We couldn’t care what you look like. You come across to me as smart, funny and quick witted. You can hold your own in conversation and I have never seen you judge anyone else. Fierra is an absolutely cool gal, and you are lucky to have her.
and vice versa.
Remember, there are many, many people who admire you for who you are. These people have seen inside your head and inside your heart, and they like you.
I am proud to say I am one of them.
Una,
I’m with TwistofFate on this one. I’d like to meet you too. I’ve admired you ever since I first met you on the SDMB, and being acknowledged by you in my early days of posting meant a lot to me. If we do get you to Dublin, or if your work brings you over here, we’ll make you welcome.
So, Twisty, stick my name at the top of your petition.
Uh, I don’t get it.
Unless I miss my guess entirely (and tonight, that’s entirely possible), that was a prime example of sarcasm, hon. 
Nope, that was not sarcasm. I’m only fourteen, I’m allowed a little idiocy once in a while. Seriously, I don’t get it.
Fears shunning from Dopers
Although I have no firsthand knowledge, I’m going out on a limb to say that Scylla must make a much better impression online than in person. If that were not true, he’d be Philosopher King of the Universe.