So far, I'm enjoying the Roomba. It has its idiosyncrasies. It can't go over power cords and we have two dressers it can't fit under. Or rather, it can fit under them but once there it can't escape.
I've run it about six times now, and it picks up a lot of dust, dirt and cat hair. It is much quieter than a standard vacuum. We have a lot of doors on our main floor, so it's easy to isolate it in a room or group of rooms and hallway.
Best of all, you must keep the floors clear to use the Roomba. And since I really want to use it, I am keeping the floors clear and motivating the kids to as well.