I knew someone on a different site who made up a whole new persona.
The screwed up part of it was that she befriended her best friend in rl with this persona, so had different emails/msn address etc. The new persona was so different that her friend had no idea.
When it all came t light I think the friendship ended over it all.
No idea why she did it. She said that she just wanted to come across different to the way people perceived her. Bit sad really.
I also knew someone (I didn't know any of these people in person btw just online) who was quite open about the fact that only about 80% of what he told people was true. His view was that considering he was unlikely to ever meet any of the people he talked to it didn't really matter if some of what he told them about himself was made up. Have no idea to this day what was true and what wasn't, apart from the fact he claimed to be single and was simoltaniously arranging to meet up with at least three different women while he actually still had a live-in girlfriend at home. .