I thought they would suck. I doubted it could do a good job and did not really understand how they worked. Got mine from woot for $8 and had to buy a charger. I absolutely love it. We have a cat and two dogs. It munches hair like crazy. It has a vacuum, edge brush, and two brushes. Thing works much better than I thought it would. We used to use an upright every weekend and ewww. Yeah our carpets got bad. Now we run the roomba 3 times a day in all rooms and it does a great job. It is loud, takes a good 40 minutes to run, and needs lots of cleaning of the brushes to work good. Charges really quick, but you need to buy a new battery every year or so. Can replace the filter bit and the edge brushes. So looking at about $70 a year to maintain.
It made a huge difference in our place. Carpets look better daily than they ever have. Every now and then i will run the upright to get some of the dusty stuff out, but I do not have to empty the cannister more than once, and it does not get much more.
Works good on the kitchen linoleum too. The vacuum part does blow furballs around, but eventually gets them. Running it everyday takes just a few minutes, and makes my crappy carpet bearable. A friend sold his because it was too annoying. We let it do its thing when we are not around or not in the same room, so we hardly notice it.
Watching it do its thing is pretty cool. It has three programs. First just spirals out till it bumps into something, 2nd goes around the edge, 3rd random pattern. It is better to confine it to just one room to get good coverage. It also has sensors for stairs and it will gently touch an obstacle instead of ramming into it. Seems darker objects soaks up the IR so it does hit darker stuff harder.