Up, incase someone else wants to share how many characters they have per MMO they play.

Usually two. Main and alt. Still, i was never into that cowardly and cheap practice, known as "twinking"... Two is an ideal number. You also cover more professions and crafting abilities this way and you can be completely, or semi in-dependent, in game's economy. Especially in games where and when you can choose more than 2 professions, like Aion for example...

I have 13 characters in WoW. One of each class, a bank alt and a random level 1 druid I created because I wanted to do a pun with its name and title.

I usually played with only 1 character that represented me at first, and at some point in the future made an alter ego that's a pure contrast from me both in gender and personality, i enjoyed roleplaying a lot with nice and right people. We had lots of fun together!