We have 3 dogs and 1 cat. The two smaller dogs and the cat don't shed much, but the larger dog (a lab) sheds like crazy. We have 2 Roombas that we got about 3 years ago when the 500 series started coming out. We no longer use them regularly because it's too much of a hassle.
First, they need to be cleaned at least daily with this much pet hair. Cleaning takes at least 5 minutes; if I just spent that time vacuuming normally for 5 minutes a day, the floors would be cleaner.
Often they won't even complete a single run without stopping and saying "Please remove and clean Roomba's brushes." That kind of defeats the purpose of having cleanings scheduled during the day (when we're at work) if it only gets 15 minutes into the scheduled 45-minute cleaning before stopping.
The Roombas will leave "Roombarf" - tufts of pet hair - on the floor when moving from hardwood/tile to carpet. Apparently the vacuum isn't powerful enough to suck all that stuff into the dustbin, so it just drags the hair along until the terrain change knocks it loose.
Every few weeks, we'd need to take the thing apart and do a really deep cleaning, as pet hair got everywhere inside. This would be a 30-60 minute job. One nice thing is that iRobot designed the Roomba to be very modular, so taking it apart isn't too bad.
One of the Roombas is completely out of commission right now because it has a faulty bump sensor. It thinks it's constantly bumping something, so it just spins around in circles trying to get free. I found a great web page somewhere (sorry, don't have the link handy) about fixing this with just a few bucks in electronics parts. I'll probably do it just for the fun of it, but that won't fix all of the above issues.
iRobot has a pet version of the Roomba which came out after we got ours, but from what I can tell, all they did was include a second interchangeable dustbin without the vacuum module that therefore has larger capacity. The normal dustbin combines the vacuum into one integrated part. I can't imagine this larger sweeper dustbin would do anything to pull the pet hair in without the vacuum to help.
For a household like ours, I would like to see a Roomba that's about a full inch taller, giving it room for a larger battery, larger dustbin, and more powerful vacuum and brushes. An added bonus for us is that since a couple of our couches are just the right height for the current Roomba to get under and then get stuck, a larger one wouldn't even go there at all.
I wholeheartedly recommend Roomba for a household without pets (or with very little shedding), but can't really recommend it with pets that shed a lot. Unless you have all hard flooring - it seems to do a lot better with the pet hair there.