Over at the PlayStation.Blog, Eric Lempel has announced that PSP Firmware v5.03 is now available to download. The minor update "improves system software stability during use of some features." Other than that, there is nothing different in the new firmare update. However, it could also patch the recently discovered GripShift exploit so if you are using homebrew, you may want to hold off on upgrading your PSP for the time being.
The official changelog for the update states "a security patch was added to address security vulnerabilities in the system software."