I have one of these from a long-ago Woot where they were $20 cheaper.
It's a neat device and for such a small vacuum, manages to pull a surprising amount of dust and debris out of the carpet.
It *really* suffers when it comes to maintenance/cleaning, efficiency of the job it does, and the fact that you cannot schedule it without buying an expensive interface adapter of some kind.
If you buy one of these, you will need to clean it at the minimum after every time it is used. There have been times where I had to clean it midway through use. Cleaning involves flipping the device over, opening up the roller housing, dislodging hair, dirt and debris from the two rollers and all their little crevices (they are magnets for getting longer hairs wound around the brushes), and emptying the debris bin/filter compartment (which usually results in getting dust all over your hands).
You will also be doomed to still pull out the regular vacuum to get in the corners and along floorboards. Due to the design of the Roomba, it has a very small path for its brushes and it cannot clean a space of 3-4" away from walls and even more for corners. So this is not a replacement for an actual vacuum. It will also take a long time to clean rooms because of the semi-random nature of its cleaning algorithms; you'll find that it will repeatedly go over some areas while others get one pass and then never again, leaving the cleaning a bit uneven. This isn't related to any sort of "smart" behavior where it identifies more heavily-soiled patches of carpet, it's just that when it bumps into something, it wanders off in another direction and eventually it's done this so many times that it's cleaned a majority of the floor.
My 530 was a refurb sold on Woot, and a month or so after I got it, the vacuum motor died. The company sent me a replacement vacuum bin under the 90-day refurb warranty. That bin has not died yet.
In conclusion, it's a neat little device that might be good if it came with an easy way of scheduling it and if you put it in a light-traffic area. They've got a very, very long way to go though before they will ever eliminate actual vacuuming from your chores, so why bother with one?
EDIT: After going back and reading through the comments here, an alarming number of people who own Roombas have named theirs and seem proud to flaunt this fact here. If the Roomba showed some sign of intelligence in its cleaning habits, I could understand this, but it's not healthy to anthropomorphize such an unintelligent device, because you end up ascribing it qualities it doesn't have--like the ability to save a significant amount of time from your cleaning chores.