Have you ever pretended to be someone else on-line?

No, but I have been impersonated.

who are they they?

Actually, I was impersonated once too. Somebody stole my skin and pretended to be me in Quake for a while. It was frustrating because he wasn't that good and he lowered my stats considerably.
I was briefly mistaken for a robot while playing Quake. I played along but it wasn't really my idea so I don't know if it qualifies. Besides everybody was in on the joke so I was only pretending to one person.

I think so, I tend to push certain points that I don't really stand for when I am on line. That is kind of pretending, sort of. I have pretended to be more of a lesbian than bisexual when I am chatting in lesbian lounges. I pretend to be a worse alcoholic than I am when I am on the AA boards.

When I've been using AOL Instant Messenger I've tried to get a taste of all the rooms on offer. Unfortunately, there are a lot of intolerant/stupid people out there so I've noticed a pattern emerging.
Hindu Singles is full of racists shouting "HA HA, you stupid Indians", Gay Chat is full of homophobes shouting "HA HA, you stupid gay homos", Christian Chat is full of Satanists shouting "HA HA, you stupid Christians".

Lesbian Chat is full of teenage boys shouting "Anybody want to cyber with an 18/f 100lbs with 38DD boobs". C'est la vie.

For all I know "Britney Spears Chat" is full of paedophiles and FBI undercover agents.

I've posed under various guises when entering these rooms. I think it helps you to see things from someone else's point of view. To fully appreciate the crap that they have to put up with. Plus, if I can talk to someone and help them to change their view about something, then who knows?

In college I was one of several people pretending to be an artificial intelligence programmed to pseudo-randomly send talk requests to people as part of someone's grad project.

I used to frequently use a feminine name on IRC, but never claimed to be female.

nope...

No, although I have been accused of doing so before.

uh...the jaff, yo

Nope. I don't have time for that. I can see how it might be fun for an evening, but I think it's rotten for people to mislead someone for an extended period of time.

A couple of times on a one-shot basis I've assumed another online identity for humorous purposes. I did once officiate an IRC wedding for someone who was marrying his regular self to an assumed identity that he'd played for awhile, that was wacky.

Once, not very convincingly, sent an "anonymous" email. My email address includes my first initial, and my last name.

I've changed my age my height and my weight

I used to play around with backdoor viruses...and i would use many alt identities to infect people through icq...muhahahahaha

I have an alias that I give to people online when they want something to call me and I'm not comfortable giving out my real name, but I always tell them its not my real name so I don't think that counts. Beyond that I'm always very honest online. It just seems pointless to deceive people.

I pretended to be a guy once. But ONLY because someone asked for advice from men only, and I thought I could help him even though I'm a female. I didn't do it to hurt or trick anyone.

i'm almost exclusively "me" online, except for one time i tried playing a character on a mud, out of curiosity. it was kind of interesting...

Hey! It's the internet. You can be whatever you want to be, and nobody will ever know!
btw-I'm a multimillionaire living on the surface of Mars!

Pretending another person is not a good way to express your opinion in any open forum.

Never!

i have pretended to be a friend of mine but never some one of a different sex.

Yes, I've done it once or twice...I've said I was older than I am...and then when I told the person that I was lying, we dated for 3 years :)

pretending you are someone else can also offer interesting insight into others. I do it sometimes usually to gain some kind of understanding, and with people I don't intend to talk to extensively (usually anyway).

I don't have to. I'm already someone else.