Roomba has several modes of operation. In "Clean" mode, Roomba cleans until it either feels that the area is complete or its battery runs down, and then it returns to its home base; "Max" mode will cause Roomba to run until it's out of battery power. "Spot" mode cleans an area of about three feet in diameter, after which Roomba will return to its base.

While running in Clean or Max mode, Roomba will occasionally encounter a particularly dirty area. It then moves into Dirt Detect mode. A blue light comes on, and Roomba makes tight figure eight patterns over the area until it feels that the dirt is gone.

Roomba has sensors to prevent it from falling down stairs; I've tested this (very carefully!) and it does work well. Roomba follows walls extremely well, and does a really nice job of covering the entire floor right up to the walls or the edge of the furniture. It can handle changes in floor height as well, and can adjust the height of its wheels to push itself off an obstacle if need be.

There are times when you want to restrict Roomba to a certain area of the house without having to close doors or set up barriers. This is why Roomba comes with at least one virtual wall unit. These send out an infrared beam that Roomba thinks is another physical wall. It's really neat to see Roomba bouncing off the empty air, and the virtual walls do a great job of keeping Roomba in its place.

While Roomba does a nice job, it's not the method to choose if you need to have the floors vacuumed quickly. My entire condo is about 1400 square feet, and Roomba takes well over an hour to do half of it. I put Roomba into a small bathroom with the door closed, and that took twenty minutes. I often put Roomba to work after dinner while I'm tidying the house, and the two of us work together quite companionably and leave the house looking very nice.

Unattended operation
Roomba can be run without your being there. My original intent was to set Roomba going just before I left for work, allowing it to do its thing and then take itself back to its Home Base.

Unfortunately, Roomba doesn't always make the best decisions for itself. So far, in my two months with Roomba, it has eaten: a large plastic spring cat toy, the bottom few inches of several different curtains and table cloths, a good five inches of my laptop's network cable, and various other power cables and cords. Generally speaking, it's actually quite good at realizing that it's sucked in something bad, and it either pauses or manages to release the object. Not always, though, which is why I'm not comfortable leaving Roomba running when I'm not home. I must admit that it hasn't yet ruined anything or damaged itself, and it would probably be fine to run it unattended, but I've become quite attached to it and would hate to come home to a disaster.

How Roomba handles furniture
Before bringing Roomba home, I was concerned that it would just run in a big circle around my furniture, and not get right in there and get the floor clean under chairs and tables. As it turns out, this wasn't an issue.