The iRobot finished charging and I ran it around the basement to clean. When I picked it up to empty the dust bin, the dust bin slippped out of my hand and the iRobot fell from a height of probably 6 to 8 inches and one of the wheels broke off.
It's still usable, as the wheel can be placed on and will still steer, but this is a bit of a nuisance. I also noticed that the plastic housing holding the wheel on -- well, it would be hard to make plastic any thinner. If no more parts break off, I'll have to see if I can get a replacement wheel housing.