you can read more about the downgrading debate
here
One Final comment for tonight:
On the Original (not slim) Sony PSP, once you downgrade from an "official" 3.XX release of the firmware back to the kickass 1.5 - you cannot upgrade to any 3.XX "official" version without very high chance of bricking your device. This is due to xtra files left behind in the NAND memory - Although you can install custom firmware so that you have the best features of both 1.5 and 3.XX
Once again, same concept i believe
