I get 5 hours gaming or movie watching out of my PSP2000, good enough for most flights.

I can get 12 hours of MP3 playback, as long as a turn the screen off (push and hold the display brighness button).

My only annoyance, is you can only charge via USB, when you put it into USB mode, which means there needs to be enough power in the battery to power it up. If you totally drain it, you have to charge it with the mains charger. It means if I go away, I either have to be careful, or take the PSU (which for some inexplicable reason has a fixed mains lead, and not a figure of 8 connector on it).