Well I had this idea that has probably been thought of before and I dont really wanna post it anywhere else hehe..
I'm not up to par on USB standards, but can a USB device connect to a USB device? If so, could you connect your digital camera to your psp and get the images from it? If usb standards allow for usb -> usb connections i think an app to pull info from other usb devices would be cool. Even if it's just a usb file manager to manage any usb device.. just an idea =)