We have two of them (one for the inside, one for the shop) and they are great!
We have three dogs and three kids in and out all of the time. We have laminiate floors and you can sweep and sweep and still not get everything. The Roomba has a rubber "squeegie" on the bottom that gets everything. You can walk on the floor and not step on any grit after it is done. You will be amazed at all of the pet hair it picks up.
We have carpet in all of our bedrooms and it is great on carpet too, plus it gets under the bed...
A couple of hints. Before you run it, get a broom and sweep the dirt from corners and under cabinets out into the open floor. It only takes a minute and makes a big difference. Also, if you have an air compressor blow it out when you are cleaning it every few times.
We have heavy traffic in our house and we only have to clean it once a week max.
It comes with electronic fences that keep it where you want it. Start it when you leave for work, it docks itself back on the charger when it is about to run out of power and you come home to clean floors...