We now own 2 Dirt Dawgs -- one for upstairs and one for downstairs (they make Roomba too). http://petoftheday.com/talk/showthread.php?t=131774 We have a combination of hardwood, tile and berber carpet. It does fantastic.

It does not like small, light-weight area rugs because the suction is so strong that it tries to suck them up. We did not buy any of the gadgets (virtual walls, home base, etc.)

No scratches on the wood floor. It sometimes get stuck in a room if there is a higher than usual transition strip between flooring. The laundry room's floor is a little lower than the hardwood in the hall. It will go into the laundry room, but can't get back out, so I just shut the door so it doesn't go there.

We love them!