Member of:
- various Disney-related discussion sites
- LA sports teams discussion sites
- Snopes
- IMDb
- OTer
- various “Gaijin in Japan” sites
Not only that, but I forgot to add any examples from Buffy the Vampire Slayer! :o
I am one of them.
I am a member of a small private Forum that broke off from a bigger one. We call it The Refuge, and we’re Refugees.
Those of us who belong to LibraryThing sometimes call ourselves *thingamabrarians. *Having the same number of syllables as “LibraryThing member” limits its catchiness though. You sometimes see *Library Thingers *which at least saves one syllable.
I’m also a goon, and a farker. I mostly read rather than post.
Do you have stairs in your house?
As an Alice Cooper fan and a member of several forums, we’re “Sick Things.”
On my local football team’s fan’s board I am in the company of “Smoggies” a nickname given to people from my hometown referring to pollution effects of the long declined but still evident chemical and oil and gas plants in the area . My user name there is “SmoginManila”
I am a Darkling-minion of Darklady(Theresa Reed), local SMOF(science fiction and gaming conventions), Yummite, JREFer and a few other groups, and they all know me as Czarcasm.
I’m a Mefite.
A goon, and also a “stealthiläinen” on a Finnish message board.
I don’t participate in the forums, but on Ain’t It Cool News, they’re called Talk-Backers.
Also, if you’re a fan of Scott Sigler (big in the AudioBook/PodCasting world), you’re known as a Junkie.
On Television Without Pity, where I am also Sigmagirl, we are TWOPers.
I think the biggest thing about us goons and SA forums is that we’re much less forgiving. There are almost no warnings ever. You break a rule, you’ll get probated (can’t post for X hours/days,) banned (have to re-pay to get your account active and post again,) or perma-banned (your account can no longer be active. if you want to still post, you have to buy a while new account.)
And since it’s perfectly ok to insult other posters and their posts, people do…and with reckless abandon. Certain sub-forums are worse than others, but it’s still not that bad. Just don’t say stupid things. 
This is the only message board I post at.
The other thing with SA is that each individual sub-forum has it’s own character (and rules, somewhat), and the traffic is so large that there are several sets of goons who rarely, if ever, interact with each other. There are sub-forums that the smartest Dopers would feel right at home in, and then there’s FYAD. Even in General Bullshit (kinda fulfils some of the same role as MPSIMS) there’s good threads - there’s one at the moment started by a vulcanologist in Iceland who is keeping the goons up to date with a volcano that looks like it’s going to erupt soon - with graphs and everything!
It skews somewhat younger than here, and is a lot more male I reckon, but it’s worth ten dollars of anyone’s money.