The first couple of times we used our new Roomba vacuum, it took longer than if we would have cleaned up the old-fashioned way, with our Dyson.
The reason? We spent the whole time following the Roomba around, watching in amazement, thinking to ourselves, "How does it know how to do that?"
There's apparently a method to Roomba's madness, as evidenced by a long-exposure photograph of the Roomba's path provided via Gizmodo.
It appears from looking at the pic that the Roomba is programmed to chart a highly-evolved route as it ingests the flotsam and jetsam embedded in our carpeting. I'm sure there's a highly-scientific explanation, but for now, I'm content with the pretty picture.
Gizmodo - Long-Exposure Shot of a Roomba's Path Shows Beautifully Organized Chaos