A few comments:
First, thanks to the OP for posting this. I'd considered it for a while, finally bit after seeing this thread. We've had it for a few weeks now, and it is awesome. We have a large yellow dog (retriever mix), and our wood floors used to feel like they had an invisible (and sometimes not so invisible) fur carpet on them. Roomba handles this mess better than we ever did using a broom and regular vacuum, and it's nearly effortless.
Second, the aforementioned yellow dog got used to it after two or three sessions and now just flat out ignores it. It bumps into his legs and he doesn't even look down.
Third, Roomba Red can do MAX mode if you have the remote (which it doesn't come with). I've ordered (but not yet received) it--seems to go for ~$20 everywhere.
Which leads me to point four: you can buy roomba accessories from quite a few online retailers. I just recently got the self-charging home base from everythinghome.com. It's on sale for $45.99 there, and includes the 3-hour charger. If you want more than one virtual wall it makes sense to just buy the full Discovery, but if you just want the roomba and the base, or even the roomba, base, and remote, this deal seems hotter to me. The base/quick charger is pretty cool--Roomba finds it by itself after cleaning and is always ready to go now, which makes it extremely convenient to just hit the button on the way out the door and keep the floors in a remarkably clean state all the time.
Fifth, if you have a young child, expect some extra entertainment. My three year old daughter calls it Roomby, knows how to turn it on and empty the dust bin, and tells everyone about it in the same tone she uses for our dog. She thinks it's perfectly normal that we have a robot in the house, and listening to her talk about it makes me feel like some small piece of life today lives up to my grade-school expectations for the 21st century. I still want my flying car, though.