The wife brought home a Roomba knock-off a few weeks back, which is a lot of fun. It's a lot smaller than a Roomba and about a sixth of the price. It tools around, bumping into shit like a distinguished mentally-challenged fellow and does the same spot approx 200 times...but it sure sucks up a lot of trash and dust. We're always shocked when we empty the box.
Definitely thinking of an upgrade to a real Roomba though, I hear they're the bomb.