I have had my Roomba for over 6 months now which has given me enough time to give it a thorough shake down.
Overall, the machine works great. It is a great way to vacuum. It is especially nifty at getting under beds and cabinets that are difficult with a regular vacuum. We tend to use it much more than our old central vac.
There are some nits about the unit.
* It is quite loud. Not as loud as a regular vacuum, but you wouldn't want to run it if you need some peace and quiet.
* Cleaning it is a pain. All the spinning parts will have hair and pet fur wrapped around them after one or two runs. The main brush is easy to clean with a knife or a special cleaning tool, but the side brush and the center wheel are not designed to be easily removed, so they get really clogged up. In fact, the center wheel will become hard to turn, which probably reduces battery life. Also, the unit has lots of small parts that can get lost easily; so take care when disassembling it.
* Extension cords will bind it up. Since the unit can get into places you normally don't vacuum, make sure there aren't any extensions cords, yarn or other stuff that tends to hide under beds and cabinets. They will bring the robot to a screeching halt.
Since replacement parts are easy to come by, I intend to use my robot as much as possible. I have my eyes on the workshop model next.