The only time I lie is in msn chatrooms to make fun of perverts (which I haven't done in a while, actually xD) or if sites ask me my age, but since I'm older than 14 now, I haven't had to do that much lately either.
and well, I did sign up for hotmail under a fake name that I still get REAL junk mail for.
but I can't think that I've lied to actual *people* online xD
[edit-- reading back on this thread, all the responses have been 'yeah for a joke'. Did anyone actually expect for someone to come out and say 'I have pretended to be a man for three years, but really I'm a girl' or 'Yeah, I'm not really a senior or Hawai'ian or a cheerleader!'? I've seen both of those, actually xD]