Features don't seem that great, I must say.  Unless you love playing the PSP on a larger display - personally, I'd play computer if I wanted larger display.

UMD Cache - ISOs For the win

Screensaver - erm, that's kinda st00pid (unless you get excited about screensavers).  The auto-screen turn off feature is so much more practical on a portable device. (I do it for my PC too; disable screensaver, and set auto-screen poweroff instead)

USB Charge - nice I guess.  Though I sometimes wonder whether constantly recharging is good for the battery.