my sis-in-law has one and they love it. They have half carpet, half laminate hardwood flooring on the first floor which is where they mainly use it and it works well for both. It will however get tangled in throw rugs and have to put the blocks near wires to keep it away from them but it works great. It goes under couches and detects wherever there is dirt and will keep going over that spot.
We watched it at Christmas dinner. There was dried pumpkin pie on the kitchen floor and it kept going back to that spot until it got that spot clean which it did eventually get that spot up. That was impressive. We figured it would have to be mopped to get the dried stuff off. Not sure how well it would do on a carpet stain though and when it decides to give up on a stain but we were very impressed with the hardwood floor and all the dirt it got up after a big Christmas dinner.
They didn't get the cheapest model, got the middle range one but if you have pets you should get the pet model. Also get the 2 or 3 year extended warranty to get the battery replaced. The batteries are very expensive.