Late, I know, but I've found that pre-gen characters can be a mixed bag. If you and your group have a specific story in mind, then it makes sense to have built characters ready to jump into, so long as the fluff and actual role playing is left up to the player. But I've also had experience with groups and DMs who use pre-gen characters to keep the players from disturbing his or her delicately planned plot, and that's just not fun.