Puzzled: the Design of Conundrums and Puzzles

I've been thinking about puzzles lately. It's partly because I recently finished participating in this year's MIT Mystery Hunt, partly because I'm working on puzzles for the Galactic Puzzle Hunt, and I've been pondering the unique experience that puzzles provide, compared to tabletop RPGs and boardgames. There's an interesting satisfaction that comes from puzzles, but it can also be at odds with some of the ways that we engage in other types of play.