At my university, most of the profs that teach our entry level programming courses use MOSS. One prof I had said that it's really good at detecting plagiarism and he automatically refers any infractions to SJA.

I always work alone so I've never been caught, but looking at the grade sheets, it seemed like almost 25% of the students were referred every assignment. I can understand the desire to catch cheaters because as I've progressed into my more advanced classes there's always a few students that really shouldn't be there because they didn't learn anything in the prereq classes.