I consider the Mp3 playback mentioned an issue for PSP buyers. I'd expect something a little more user friendly from Sony, Mp3 playback should be seamless. Hang on do you just have to rename mp4's? Or do you have to rename Mp3's too?
But the battery life is of course the biggest issue. I know how much it can be a pain, from my iPod. I'd hold off from buying one until this is fixed (or maybe it won't be an issue by the time of release)