They work great on all floors - carpet, tile, & hardwood. Like others said, they don't do a deep clean, but are great for maintenance. They tend to get stuck every now and then on rugs, HACP vents in the floor, under the lip of the kitchen cabinets, etc. Generally, they are pretty good at getting themselves unstuck. The battery died on ours, and is expensive to replace.
All in all, we have liked ours a lot.