For a little while there, owners of both a PS3 and PSP could use their console to download certain games designed for both systems, then easily copy them over. It was way better than using the PSP on its own.
Now, for some reason, that feature is missing.
Since updating to the latest firmware, users trying to copy over certain games - like PS1 titles, which play on both systems - have found they can't do so. UPDATE - Seems they can if they don't install the game on the PS3 first. You used to be able to copy regardless, but now can't copy if you've installed it.
It's unclear whether this is a glitch, or whether Sony has removed the capability. It'd be a shame if it's the latter. Using the PSP's online interface these days is like pulling teeth, which I guess is why they introduced the copying in the first place!
PS3 firmware 4.00 limits PSP game installation [Shacknews]