That everpresent "Mathematica" blurb on the screens doesn't represent any kind of site category, I don't think; the whole site is driven by Mathematica behind the scenes. The Mathematica link often visible looks like it goes to some sort of representation of that behind-the-scenes stuff, but that's just a guess.
Oh ok, thanks for the info. Since I saw a big list of categories at the end of the screencast and remembered that "Mathematica" was there all along, I figured there was something to it. I just have a hard time believing that that kind of results can be achieved without more information than the keywords.
