1) I'm a writer outside this forum and I have a few books in the making. Roleplaying helps me practice, and it can also be kinda fun. Alright, so it's mostly for the fun part. XD
2) Depends! If it's especially sexual it'll arouse me (duh), if it's cute it'll make me feel snuggly. If it's especially well written I'll probably feel a bond with the person I'm roleplaying with, and of course it cheers me up in general! I'm usually quite miserable.
3)Uhm. A lot of people here seem to only be able to play characters that they relate to, which I see as a major flaw. The best Roleplayers on this site in my opinion, are the ones that can play as a variety of intriguing yet quite different characters.
As for me, I'm not sure. Perhaps I try not to put too many of my own traits into my characters, but I could never be certain it was working. But I guess it makes it easier to play as someone you relate to?
So yes and no?