Let's see.  I've played up to level 3 on Medieval (UMD I own), world 3 on Loco Roco (before I found out that I had the screwed version), about 1 track of Wipeout Pure (I suck at racing games), about 30 mins play on SNES Zelda and some KETM (homebrew).
I would probably play FF7/9 (already played 8) if I had them.

Otherwise, I've basically watched all my anime on the PSP :P
Interestingly, my Medieval UMD is always in the PSP.