Squee, once you figure out irshell (it takes a bit, have patience), I think you'll really love it.  Main things I love about it are the pmf player and file browser in it, the pdf reader included (I know, you can find it elsewhere, it's just handy having it bundled) and the ability to turn off audio channels in games and replace it with your own music,  You can mute the in game music and play your's from the memstick.
It's also a full xmb replacement, you can run everything from it and never need your psp's xmb interface.