Tereas Lo has posted an excellent article highlighing sentiment cycles. It's ironic that she uses the dry shipping industry as an example, since it is a sector I played on the way up and have recently been playing as a short on the way down (I've already shorted DRYS three times in the last two weeks, and just shorted again today). If you understand these cycles, you will make loads of money and not fall into the traps that many investors get caught in.
As you guys know, I am big on accumulation and distribution patterns. It's an excellent way to catch the euphoric up and panic down moves.