Unfortunately you can not at this moment in time. However their is meant to be an update for it so im guessing you can back it up. Only problem with updates is sometimes according to other users they have reported they lost their entire save thus having to start again.
You "used" to be able to backup your saved games to USB and move them to your other PS3's, and yes I have 3. But because people were hacking the saved game files for Call of Duty and I assume a few other games, Sony saw the work around as locking the saved game files so now you cant back them up.
its bad enough you cant log into other PS3's and have your same games, but now they put a terrible fix in for a problem that needs to be addressed in their coding. Ohwell.
Long story short, pick the PS3 you wanna play that particular game on and stick with it.
There only way to transfer your save would be to connect 2 PS3s with an Ethernet cable and use the data transfer utility. You will also need to establish a wireless internet connection on both consoles. But that would mean totally erasing everything on the PS3 you're transferring the data to. And you cannot swap hard drives, if you do the system will ask you to format the different hard drive, thus erasing everything that way. So yeah, why not just start a new game? You're able to gift one car a day.
Monetary wealth is never destroyed, it is merely transferred. Recessions do not happen by chance, they are planned.
Not being able to backup the GT5 save is a joke. A bad bad joke. It takes a lot of time to grind, your levels, cash, cars everything. To add insult to injury, the online servers doesn't save and keep track of your progress as well.
Without syntax and grammar, human language would not be any different from the chimpanzees that shout repeating sounds. ~ Phillip Tobias