Some folks have figured out how to enable some hidden functionality in the PSP, including a limited web browser.
http://www.fumanchuu.com/pspdev/
It's all very preliminary, and I don't expect it will be possible to do much hardware hacking on the PSP, since it uses multiple high-integration SoCs, etc., but there has been some work done on using more standard generic memory sticks and so on. It would also be nice to be able to hook up a stock external USB DVD-RW drive rather than rely on the built-in read-only cartridge drive.
