Apparently some PSP games have been pulled from the PSN store (Motorstorm and Hot Shots Tennis because of an exploit/hack), and removed from all download lists - if it's not already on your PSP or Vita memory stick, you ain't getting it, in other words. They'll probably go back up at some point, but that and the fact that I have already bought a handful of PSP games got me to thinking:
According to their TOS they can remove the ability to download games at any time, and don't necessarily have to refund your money or credit your account (at least in the US). There's no guarantee that the April firmware update (which supposedly fixes some things on the browser and updates Vita/PSP compatibility) won't "shut out" certain games from being played on the Vita, whether it's because of rights issues or exploits or whatever. Particularly the ones which aren't on the official BC list that folks have been transferring via PS3.
So if, like me, you've been buying cheap PSP games to play on "dat screen," I'd be careful about updating the OS whenever the firmware releases. Check around on the various message boards first to see if anything's no longer working, or transfer has been blocked. If that happens, you might just be shit out of money/luck. I'm personally going to hold off on buying any more PSP stuff from the store until the update happens, and see what shakes out then. They certainly have a history of snatching shit away without much (if any) warning or explanation.