YMMV, but I actually look forward to airtime as downtime -- an opportunity to just sit back, relax, listen to music, have a drink or three, and, literally, watch the world go buy. Most times, I'll wind up falling asleep, which I also find a productive use of my time.

On super long-haul (SFO/HKG, for example), I'll load up my laptop or netbook with movies and television shows that I want to watch, but I find I rarely watch more than one or, at most, two, in-flight. Though I enjoy reading, I'll rarely do it on an aircraft. On UA, Channel 9 is often interesting, particularly with those pilots who like to do short lectures about the plane, or describe points of interest. They're always aware they're talking to flying enthusiasts, i.e. the typical FTer, so their talks are always fascinating.