Thumbs don't work properly for me - think it's a caching issue. I've cleared cache etc., but after I click up/down vote it sometimes resets to nothing, or just sticks on what i've clicked (further/change of clicks/other people clicking doesn't show up)
I think the problem previous was that they were basically invisible so you couldn't tell which was which. The problem now is just that they look shit.
Hopefully the flat grey ones will be non-shit looking and usable.
I don't think it needs a tooltip or owt, it's pretty obvious what thumbs up/down does. So long as they are recognisably thumbs up/downses.
But yeah if the newer ones look shit then rollovers is probably the way to go. Be nice to overhaul all the icons with flat versions. The cartoony semi-3d ones are looking a bit dated now. Might do that if/when I'm bored enough if these ones look ok.