I've had a love/hate relationship with our Roomba for about 5 years. It's the Roomba 580 model.
As mentioned above, when it works, it works AWESOMELY on hardwoods / area rugs for picking up pet hair. It also travels under our living room couches, which is HUGE for keeping the dust bunnies down.
That being said, I had to send it in for a total overhaul to a third party shop, just outside of warranty. It cost me just about as much as buying a new one.
Since then, it's worked well. I've also "invested" in a third party sealed gearbox for the brush drive. My original one failed due to dog hair intrusion.
For us, it's really important to empty the collection chamber and clean the brushes frequently.
Here's the site for that repair and aftermarket stuff:
http://www.protechrobotics.com/index.php
Certainly still have to break out the old vacuum cleaner weekly, but the Roomba maintains well.
Dave