We started using our roombas after Zobert stopped soiling the carpet. We have one for our bedrooms and one for the main room. When we run them once a day it keeps our carpet in great shape. If I pull out the upright on a weekend it does not pick up much, so they are doing a good job. We have two dogs and a cat, so pet hair is a problem. The roomba handles the hair well, but it can work its way into the gearbox that drives the spinning brushes. At times the roomba will error out because the brushes get clogged and worst case I need to crack the gearbox open to clean it out.
The gearbox does have a flaw. There are three gears that pass through the wall of the gear box to drive the brushes and connect to the motor. There is no seal on these areas so dirt and hair can work its way in there. Opening the gear box voids your warranty. They do make roombas with a bearing on the gears to solve this issue, but some models still are sold without bearings. I decided to add some.
On the robot reviews website vic7767 has a tutorial on how to install the bearings and he also sells the bearings. I got two sets of bearings and picked up some step drill bits and worked on them sunday. It went pretty well, but a few holes got drilled out too much. I put a layer of electrical tape on the bearings and they fit very snug. When the gearbox is assembled it holds it all in place so it should not be a problem. Both roombas are working fine and time will tell if it was worth it, but I am pretty confident.
We also have an improved aerovac collecting unit on the way. It is said to make a huge difference. Will let you know when it shows up.