Merlin Mann has been tearing it up about Getting Things Done over at his Back to Work podcast on the 5by5 Network. Around an hour and five minutes in he talks about the joy of a modern five hour flight is that you can still have five hours of uninterrupted thinking time.
I have been trying to put that into words for a while now (usually when on a plane), but he does it much better in just a few minutes.
I highly recommend you take a listen to think about how to use your next five hour flight.