I just returned from a week in Alaska traveling on AMHS ferries and staying down in Seward for work. I read Hacking the PSP and a review of the book will be up on Geek.com shortly. I discovered that I was only able to play World Tour Soccer and Spiderman 2 UMDs with 6 others not working on my trip and was getting worried that my UMD drive was failing. I hunted around online, but nothing I found solved my problem and the only solution that looked viable was to send the PSP back to Sony. This wouldn’t work for me since I bought mine used from someone on Craigslist.
I then took a closer look at the actual UMD disks again, I had already cleaned them off and blew out any dust. I found that the clear plastic on the front side, side opposite the opening for the laser to read the disk, along the top was pressed in a bit on the disks. I shook the UMD and it still had plenty of movement, but then bent them around a bit and was able to get the clear plastic to line up again with the rest of the UMD. I popped in Napoleon Dynamite and it worked like a charm. I was very happy after testing all the rest of the disks, but also quite surprised that the UMD drive would be so sensitive to not function with the plastic just slightly, about 1mm, pushed in on only one part of the disk. I now have to watch how I store the disks a bit better and cannot put my headphones into the same case without some kind of disk protector on the UMDs.