There's some interesting analysis of the math behind Spot It! on stackoverflow [1].

That post mentions the Fano Plane, which, incidentally, I first read about in the book How Not to Be Wrong by Jordan Ellenberg, a mathematician quoted in the article about Set that started this thread. In the book, he uses the Fano Plane to explain how to pick numbers for a specific kind of lottery.

[1] http://stackoverflow.com/questions/6240113/what-are-the-math...