I've had one AIM screenname the whole time I've been online, and I won't change it for the same reasons Vampy pointed out. You change the name, and then, people lose touch with you. Also, I use mail preferences on my account, so every time I change a name, I'd have to redo those preferences, and THAT is a pain! Therefore, it's much simpler to keep the name I have.
I also concur with some that it's stupid to change your username fifty times over. What's the deal with that? We all will figure out who you are eventually just by your writing style. I can see if you're bored with a username. I've gotten bored with mine from time to time. I've also contemplated a slight change to Oceangurl, because a friend used to call me that, but I never actually did it. I just don't see the point. I'll always be Oceanbreeze, and that is fine by me.