Update: The official European PlayStation Twitter account has offered an update on the update. It has been pulled down for the time being.
Sony also reached out to Joystiq with a statement saying, "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 apologise for the inconvenience."
Original story:
For the time being, it's probably a good idea to decline the latest system update for the PlayStation 3. Many users are reporting bricked consoles after updating.
Not all users are encountering problems after updating, but if Sony's official message boards are any indication of how widespread the issue is, it certainly couldn't hurt to wait.
We'll make sure to update this story when Sony responds or makes a suggestion about what to do.
[Source: PlayStation 3 Forums via Joystiq]