I see lots of "user312" and such, they are similar and make things difficult. I think it would be nice if we encouraged these users to pick a more personal name.
We already have a bar that shows the first time, and Pascal suggested that we repeat the reminder when they get more reputation.
I think that a more stackoverflow-y way of handling this is to give reputation points to people the first time they change their username. If we want to be picky about it, we could restrict it to changes that don't match the user[0-9]* pattern. This sets the right incentives, in a way that I think will benefit everyone.