Did you download the PS3 2.53 Firmware Upgrade? If not you can download version 2.53 here.  According to Sony, the

PLAYSTATION®3 system software update may include security patches, new or revised settings and features and other items, which will change your current operating system…

The Playstation PS3 2.53 upgrade is right on the heels of version 2.52 released less than 1 month ago on November 5, 2008.  Sony announced the Firmware upgrade last week but did not go GA until today.