Gamecard games save your games on the game card. Downloaded games, it looks like your games are saved within the application itself on the memory card. It looks like you need to connect to a PS3 or computer and back up your data through Content Manager.
if your trying to back up just saves and not your whole psv.. I do not think there is a way, i have been tryign to figure it out because I get most my games from gamefly, and sometimes I just want to return a game and try a new one, the come back to the previous one with my old save, but it looks like you cant do that with vita games.. atleast yet, hopefully it wont be like this forever.
If people know a way to back up JUST SAVES and keep them, like you can on ps3, let us know!
Gamecard games save some data to the memory card to assist in load times. Game saves (and DLC) are saved to the game card with most games. This is why trophy support is disabled if you try to play a game registered on someone else's PSN account.