Last I heard, he still flies coach
Maybe he has changed, but years ago Gates always flew in coach class. He was into high performance sports cars but not airplanes, although he did invest in the Eclipse 500 jet.
Paul Allen, on the other hand, owns quite a few planes. I don't know if he flies them himself, but he's more my kind of guy. Branson is cool beyond words. Fossett, while not a billionare, lives a life I can only imagine.