YES YES YES! This is a WONDERFUL idea! I've wanted to be able to chat encrypted with a friend of mine forever! We've tried encrypted e-mail, but thta's a pain in the butt. Encrypted AIM would be a dream come true!
you can always just send each other PGP text. Of course AIM+ could make this happen behind the scene's I imagine. Lot's of work though sicne AIM+ would probally need to keep track of all the public keys. ouch. Easier just to cut and paste with the PGP tool.