I've been thinking about this for a while now. Have you ever noticed that some MP3s, when played in the XMB, either suddenly stop playing and appear corrupt or appear corrupt right after playing? I have two example files attached. (They are both crappy songs, but the only ones i could find with this!) You MUST not fast forward or rewind the songs while playing. The first one is the theme song to the cartoon, Freakazoid. At the time 00:42, the song will suddenly stop playing and appear as "Corrupted Data" and will not play until the menu is exited and another media bar is accessed. The second one is I Ran Over The Taco Bell Dog by Adam Sandler. At the end of this song, the file appears as "Corrupted Data", just like the first. These files sound fine when played on a computer.
Just extract the ZIP file to your PSP. When playing these files, set Group Mode to off so the groups do not skip to one another.
Just thought this may offer an opportunity for another exploit.