My sister has one and is in love with it. Can't say enough good things about it. She also has a Roomba and thinks it's great too.
I haven't ever seen either one, and, IMO, they seem a bit OTT.
Saying that, she has 5 kids and has now gone back to work full time, so it saves her doing it when she gets home. I only work weekends, have a small house and 2 kids, so it isn't a huge problem for me to vacuum, and I leave the mopping to Keith!