A new PSP Firmware update will be available to download soon. The minor update will address system software stability issues during use of some features. Other than that, nothing new has been added to the software update. You will need to update to the latest version in order to access the PlayStation Store on your PSP.
PlayStation.Blog post by Eric Lempel:
A new PSP firmware update, v5.51, will be released soon. System software stability during use of some features has been improved.