I'm not American, so I'm damned if I'm going to call them "movies" all the time! anyway, I've barely used the GP2X for this feature since I bought it, so I thought I might as well see how well it worked. I dug out a DVD more or less at random (it was Oliver!) and ripped it to Xvid using AcidRip, which has the inestimable virtues of being in the Ubuntu repositories and of actually working out of the box.
Having copied it to an SD card, I bunged on the movie player (the built-in one) at standard power. Not bad at all, actually. As we know, the sound quality through speakers is pathetic, so it did need some headphones, but apart from that and the slightly restrictive vertical viewing angle of the screen there was no problem. I wish the Start-to-quit button had an "Are you sure?" step, though.
I must admit, I'm not entirely certain what the other two power settings in the movie player are for. If you turn it down low for economy the video stutters too much to be remotely watchable; and since it works fine on normal why would anyone use the extra power setting? Ah well. I was wired up to the mains,* incidentally, so I have no idea what battery life was like.
* Okay, not me personally. That may disappoint some of you...