Are robot vacuum cleaners any good yet?

So spring is nearly here, and as always, that means massive dog shedding in the house. I've been vacuuming every three days or so and it still isn't enough, so I thought I'd look for a better way.

The last time I looked at Roomba's and similar machines, I thought they were kind of expensive given how limited they are. But I'm seriously thinking of giving them a shot now.

Anybody like or hate them? Can they cope with lots of dog hair? Can they even catch up to dog hair that floats around with the breezes? How good are they at learning room geometry now?