Bringing up this old thread, but thought I'd put my review in. I have 2 Roombas and a Dirt Dog for the garage. I live in Colorado, and have 3 cats and 2 dogs, and they all shed like crazy. The Dogs live in the garage and backyard, while the cats are in the house (and go outside). I also have 3 kids (11, 9, and 6), there is plenty of stuff tracking into the house. I have a 4400 sq foot house (3000 sq ft house + 1400 finished basement) with hardwood and medium carpet.
First, the Dirt Dog is pretty awesome. It is very low maintenace compared to the Roombas, and does a great job in the garage. I have a large garage, and the Dirt Dog can clean just about everywhere. Its nice going into your garage with bare feet and feeling a clean floor. Does a good job of picking up all the dog hair as well. Highly recommended.
The Roombas also do a good job, but they are more maintenance. My cats shed so much, I have to use the Roomba every 2 days in our main family room, where everyone hangs out. I have to empty the bin and clean out the filter every run. I found the easiest way to clean the Roombas is to use a regular vacuum to suck out all the hair from the brushes and ends. I use needle-nose pliers to quickly rip out the hair that gets coiled around the ends of the brushes (this is the fastest method - believe me) and under the yellow bearings. To make this whole process fast, I keep my shop-vac all set up in the garage, so I can quickly clean the dirt bin and filter chambers. The shopvac is also great for cleaning out the brushes. This whole prcess takes about 2 minutes per Roomba. While it is work, I still think the Roombas are well worth it. Every few weeks, I'll give them a more thorough cleaning, such as cleaning under the side brush, and under all wheels.
I've been using the Roomba for about a year now without any problems, or having to replace any parts or filters. I think that using the Shop-vac to clean them out every run has kept them running strong.
I find that they work as well as a normal vacuum on carpet, and even better than my other vaccums on area rugs. I can vacuum a room with our Hoover upright, and then send the Roomba in, and it will still find plenty of dust and debris. I have a pretty clean house, all things considered, and I'm always amazed at how much stuff the Roomba pick up. I hardly use a normal vacuum at all - just for stairs and in places the Roombas can't reach, and that's only every few months
As a poster above said, the Roomba also gives you a good excuse to keep your house generally in order. After I start the Roombas, I spend about a minute picking things off the floor. I would have to do this with a normal vacuum, so no big deal.
So, overall the Roombas do a great job of picking up dust, debris, and cat hair. However they do have to be cleaned up every run (at least that's what I do) and they are not maintenance-free. I've set up a small Roomba cleaning station in my garage so I can get them all cleaned out and ready to go as quickly as possible, with the help of athe shop-vac. If you spend too much time cleaning them, then it gets counter-productive.
I'll soon be getting a third Roomba so I can have one on each level of the house, and can spread the work around. The upstairs and basement only need to be vacuumed once a week, but the main floor needs it every 2 days.