i used to hate mirrors till i got really used to riding with one. now i feel helpless without a mirror. i always fully turn around before making a move, but having that little subconcious preview of whats behind you is helpful.
plus if youre riding dirty you look a lot less sketchy peeking into a mirror to see if a cop is behind you than turning completely around to check.
that said, aesthetically mirrors are fucking retarded, but on a utilitarian daily rider its a pretty good idea.