I ain't never vacuuming again!
Yes, it's an expensive toy, but I love this little guy! It takes about an hour and covers every room in my home, including going under the bed and sofa, sweeping under the table in the kitchen, etc.
Of course it does not leave the floors and carpets sparkling and pristine - if you want ready-to-sell-the-place/get-your-deposit-b
Early Roombas got very mixed reviews. They were pretty stupid and not terribly efficient. I bought a Roomba 770. It's still not that "smart," but it finds its way around corners and through obstacles, like chair legs and half-open doors, with a little bumping and circling around. When you watch it work, it seems to be just zig-zagging randomly in and out of rooms, but eventually it covers pretty much every accessible square foot. And it automatically goes back to its charging station.
Having watched it once, I'd feel pretty comfortable leaving it to clean while I'm not home. You should do what you can to remove obstacles (put wastebaskets and lamps up on chairs, make sure there are no tangles of power cords/ethernet cables strung all over the place), but as long as you've made sure there is nothing that will seriously muck it up, it really is a turn-on-and-forget-about-it robot.
Will let you know how it's been working out after I've had it for a while.