3. There seems to be an exploding interest in software that'll handle this function within iTunes, but I don't know about this one. I'm looking for something that's a little more complex (using alogrithms and such) in how playlists are built, rather than focusing on only BPM's, which BeaTunes and Tangarine aparently do. A program called The Filter looks promising, as does Soundflavor, but they only work on Windows currently.
Tangerine! Create Magic Playlists