I love love love mine. It has massively changed our home. We now have the motivation to keep the floors clear of clutter.
It hoovers my living room/dinning room 1-3 times a day, the rest of downstairs daily and upstairs as and when we need it.
We thought we would still need to hoover once a week but we don't. We sold one of our Dyson hoovers and now seriously considering selling the other as it sits unused most of the time, and we have a handheld for stairs.
The roomba actually cleans better than the Dyson. you can run it over What looks like a spotless floor and it still has dirt in the box at the end.
You do need to empty it pretty much every time you use it though, or at least daily. that's In our house anyway but it gets heavily used - family of 6, baby/toddler dropping food etc.
we have now bought a scooba and are equally impressed.
We bought both second hand off eBay so didn't cost quite as much. 