I have a 550 "Pet edition" Roomba, and it works great. I have a single cat (who admittidly doesn't shed that much compated to most cats). I have to clean out the rollers every once an a while, but it's still better than actually vaccuuming. While it can't get into a few areas (behind the garbage can is a big one) it generally works great. I think it does a better job than me (because I don't take any time to move anything).
The biggest problem I have with it is that when it decides that it is done a room, it tends to hide. It might be under the middle of the bed, or tucked under the sofa in the back corner, but it's rarely in a spot where I don't have to get on my belly to retrieve it.
I named mine Saul after Saul Goodman. Better call Saul!