Mine is a Roomba brand (more expensive than the e-bay ones). It's very effective on timber floors and carpets - we run it every day, and only every have to vacuum manually about once a month.
It struggles a bit with the layout of our house, and often can't find it's way back to the dock, but we just carry it back when we get home.
It's capabilities to drive over/around things is amazing - I can't see why NASA wouldn't use it as a MARS probe it's that good.
Check the height of the unit vs you furniture though - ours just misses out on getting under the couch, which is a shame.
We have the language set to french, so I can say I have a french maid