PSP is heavily overrated, from what i've heard the games are pretty boring and most people just use it as a media center, also UMD's never kicked off because who wants to pay for a movie that you can only watch on a PSP, seems a bit silly if you ask me. If PSP is doing so well why is the GBA SP and NDS Lite beating them by sales hands down in japan
UMD is for those people who want to be able to watch movies anywhere they can bring their PSP. Who cares if you can't place them in a DVD player? Doesn't seem silly at all to me. And hey, if you get bored of watching videos, you can always play your games or listen to music.
Also, for the record, the PSP is a media center. Do media centers not include games? Based on my knowledge, they do, unless we are talking about school libraries, where they ban any usage of games, but y'know, it's for the better. We need that place for research, not to wait on some guy to finish his game of Halo.
Maybe the manufacturer of the game is writing the disc at too high a speed if you're experiencing problems with a disc that has less than a noticeable mark on it.