If you have a dog hair problem, then I'd suspect that the Roomba won't be a good option for you.
I can't imagine that it's capacity and suction would be sufficient to get it up.
I bought one for my parents a couple years ago, and they love it, but they don't have much mess at all. No pets, not much dirt gets tracked into their place, and they don't have that much space to keep clean.
Mostly they just need something to follow my dad around and clean the crumbs up since he won't use a plate!
Anyway, they love it, but they don't have much to clean. I think it works best in situations like that.
For pet hair, I have a Dyson, the Animal model (it's the purple one). It works really well.