In addition to features such as new content and stereoscopic 3D, Sony have also announced that there will be a feature that all of the titles in the "PSP Remaster" series can take advantage of.
Gamers who own both a PSP and a PlayStation 3 version of the respective game will be able to use save data between both pieces of hardware. This means that you can play the game on PSP on the go, and transfer the data to your PS3 when you get home. This feature will work across all the PSP Remaster titles, it is not yet known whether this would work the opposite way.
Another feature that some games will also be able to utilize is the ad-hoc gameplay, through the "adhoc party for PlayStation Portable" mode on PS3. This however does not work at all on the early 20GB PS3 model, CECHB00.