We have hardwood floors also (tile in the bathrooms and laundry room). We've owned two Roombas and now have a Neato and I really prefer the Neato. It basically maps the room and goes over every spot. The Roomba we had was like a drunk person with a vacuum, aimlessly wandering around, and you hoped it got every spot.
The only drawback is that it obviously cannot get right up into corners or under furniture and that's usually where the dog hair/dust goes. A quick sweep with the Swiffer takes care of that, though.
We got the Neato on sale at Target, so check their sales.