Yeah, but I don't really want to add rep - just see it - and then you have to click somewhere else to make the rep box go away without adding to rep. A hover tooltip just seemed like it would be a convenience. Certainly not something that I would put into a "pisses me off" category though.
It's faster than viewing the profile. ;) A hover tooltip would be nice however it would just add complaints from those that already dislike them while adding a minor convenience to those that don't.