If you are flying any of the 'big' ones, United, American, Delta, US Air, Continental, check this site out. Heard about it on the radio, looks very helpful.
On my recent 13-hour flight back from China, I was sitting in a window seat. Unfortunately, I had "Rock Man" sitting between me and the aisle. I called him that because he literally did not move for most of the flight. Being the considerate person that I am, I thought I would wait until he got up to go to the lavatory. Well, after a while, my bladder just could not take it any more, and I had to ask him to let me out . . .
Neat site Dan. I found a typo on the page and sent an email off to the author of the page. Next time I fly on a "real" airline, I'll give this site a look see.