I bought a Roomba 560 for my loft which has hardwood floors throughout and a tiled floor in the bathroom. I schedule it to run three times a week (Mon, Weds, Fri)whilst I'm at work and it does a bloody good job.
I have to clean the brushes, filter and dirtbox after every run (no idea where it gets it all the crap from) but this only takes five minutes. I change the brushes, filters and sweeper brush every six months.
I have two Roomba's, both 560's. One for upstairs and one for down. They work great although after a year Rosie is becoming a bit temperamental (Yeah, I named them), I need to clean her brush sensors better. But they work great and do a good job. BUT if you have more then two rooms, I would recommend getting another one, they do have a tendency to get lost if there are too many rooms.
Now, Roomba does have one flaw, BLACK! If you have black pattern or dark brown, then they think it is an edge and back away from it so they don't fall. This is not good, but I can point you to a website that will show you how to fix this problem --- as long as you don't have any stairs for it to fall down.