So, how does it work? Not quite the way that I expected. I had expected it to more or less map out the perimeter, then start a sweep pattern. That may be a bit much to expect from relatively cheap consumer-level robotics at the moment, though. What it actually does is wander around bonking into things, although I don't know for sure if that's the intended mode of operation or just a result of the crowded state of my apartment. You can watch it in action (warning, almost eight megabytes). My little digital camera doesn't do sound, sorry. Subjectively, it's nowhere near as loud as a normal vacuum, more like a little dustbuster. I can mostly tune it out but I'm pretty good at ignoring noise. Your mileage may vary.
What it is really good at is getting itself out of jams. If it gets wedged under something (it's less than four inches high and not much more than a foot across) or in a corner, it will figure a way out. It doesn't do so well with electric cords that it can get hooked on, but if you police an area quickly before starting your Roomba, you really can just let it go without supervision. If it gets stuck so that it can't escape, it will give up and shut itself off. And as it bonks its way around, it collects a surprising amount of dirt. Yes, it may take an hour to do an area that you could do in less than ten minutes, but who cares? You're sitting there reading a book or whatever while it works. I can already tell that my apartment will get vacuumed a lot more (like once a week rather than once every month or so) now that the Roomba is doing it rather than me.
It will run for a couple hours on a charge, long enough to do a couple moderate-sized rooms. Speaking of which, if you want it to do multiple rooms, you're probably better off putting it in one room, then taking it to the other room when it's finished with the first if there is only a standard doorway between the two. As it bonks around randomly, it won't find the door very often, and even when it does the odds are that it will turn around and go back through the door soon — your mileage may vary depending on how crowded your home is.
Roombas come with items called Virtual Walls. (Normally you get one, but there's a promotion right now where you get a second one free with a Roomba Red.) They are infrared-based, projecting a beam which the Roomba detects and treats as a wall. They sound wonderful but in practice they have some drawbacks. They work best for blocking off a doorway, where you can hide the emitter on the far side of the wall from the room where the Roomba is working, projecting the beam across the doorway but not into where the Roomba is. Besides beam spread, they also suffer from reflections, the same reflections which allow you to use your infrared remote controls even when they're not pointing anywhere near the device you're controlling. If you try to use Virtual Walls to block off part of a room, for example, the boundary becomes very approximate, and the Roomba is likely to stop and turn around at random places which are nowhere near where you thought the beam was. Sometimes a real physical barrier made of a couple spare cardboard boxes works much better, as demonstrated toward the end of my little video.
Overall, I like my Roomba Red. Obviously, since I just got it, I'm not in a position to evaluate its long-term reliability yet. I do think it will repay my investment in it, though. I will be recommending them to my mother, who is getting old enough that vacuuming is a bit much for her. One key part of being happy with your Roomba is knowing what to expect — I was disappointed when I first turned it on and found that it bonked around randomly. Only after watching it for a while did I realize that it was doing the job, and keeping enough track of its environment to know when it was done. Hopefully, after reading this review, you won't have to go through that little twinge of buyer's remorse. :)