I typically don't reuse characters because I have that weird way of thinking that limits a character to one universe.
I think I lose interest in them if I have to reuse them. Sad, though, that a lot have just... died. I understand the idea of reusing characters, especially with RP's that simply don't lift off and give an individual time to develop their character. And, getting attached to ideas.
For me, I think it's getting attached to the idea as a whole, rather than just the idea of a character. I have a lot of ideas for characters, but they usually spark when given foundation to build up from, i.e. a roleplay/story's plot, instead of just spawning out of thin air. I normally join, and if the plot the GM provides interests me enough, then the character ideas come.
(I'm that weird person who picks the appearance first and foremost, likely the most trivial part of a CS. It just bugs me because I usually take forever to find something and it's so much easier for me to match a personality + backstory to an appearance if I've already got one locked into place. D; Does that make me weird and superficial?)