Mindset is a research program to train software to recognize commercial pages. One application of this tool is that you can try to exclude commercial pages out of the result set.
Of course, if this is as good as spam filtering, people will only be partly happy with the results. And yes, there are many commercial Web sites trying to pass out as non-commercial. Everyone is out to sell something, afterall.
Interesting question: would you ever want to do the reverse, that is, exclude non-commercial content?