I was very suspicious of this when I first saw it. But then I went to Ambrosia's website and it was actually there, so I downloaded it just for fun, even though I didn't really believe it. I had a feeling it was an April Fools prank. Then I read the comments on the review on macteens and my doubts were confirmed. I'm running it right now just for fun, though.
Read the Read Me file. It says that it take about 10 minutes for them "to get an accurate reading." Keep the program open for a while and it will work.
P.S. The easiest way to tell this is a hoax is to quit the application before it's done. If the cloth ball hasn't already started going over the screen, the screen immediately gets brighter, and if it has started, all the "uncleaned" spots suddenly are bright.