UPDATE: Sony has identified the problem and will release new firmware next week.

Sony loves to release new firmware for its PlayStation 3, and aside from the neverending jokes about the neverending update cycle, the process usually goes smoothly.  Unfortunately, the initial release of system update 4.45 is causing serious problems with a number of PS3 owners.  Users report that the update is disabling their consoles, locking them at a perpetual startup screen with no solution in sight.  Joystiq has an official statement from Sony on the matter.

"We are aware of reports that the recent PlayStation 3 system software update (version 4.45) has caused the XMB to not display on a small number of PS3 systems. We have temporarily taken 4.45 offline and are investigating the cause of the problem. We will announce when the system update is available for download as soon as possible. We apologize for the inconvenience."

Impacted users report that their PS3s boot to the background of the XMB interface, but do not offer any actual menus or input methods.  No restore, no redemption.  This update was supposed to enhance system stability.  Oops!  Talk around the Internet is that this issue primarily impacts consoles with upgraded hard drives, although there doesn't seem to be a definite pattern regarding brand, size, or other factors.  Something must be an underlying issue here.  If you use PlayStation Plus's auto-update option, do not accept this update if prompted.  Wait for Sony to fix the problem and reissue the update.  Not everybody who has installed the update has been impacted, but do you really want to take that chance?