Nintendo DS cartridges have to be authenticated and now look at that system - so far I see two completely different ways of uploading homebrew to it - via the cartidge slot with a small modification, and via wifi.
I wouldn't be suprised if the PSP goes the same way - ok, we probably can't mod the UMD drive, and even if we could, we couldn't write out UMD media, but the memory stick and wifi may be open to attack. People can already crash the PSP (what seems like a buffer overflow exploit), so if the PSP SDK is flying around this may give them what they need.
One thing you may have to do however is obtain a PSP before new bios versions come out. As no doub't Sony will be watching and patching any holes as they appear, and since the console can auto-update itself over wifi, this could mean you can't use it to browse the web without it updating itself, which could kill the holes. Then again, maybe it's possible to fake Sony's update website and get the PSP to download a new (hacked) bios without any protection in - that'll be nice.