Sony has apologized for last night's firmware update issue, and says it is currently investigating the cause. A new version of firmware 4.45 update will be made available once the problem has been rooted out.
"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," a PlayStation spokesperson told Kotaku. "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."
The update, which went live last night, was supposed to add trophy notification options and improve overall system stability. Some members of the PlayStation forums, however, said the update made their consoles completely unresponsive. It was subsequently pulled.
Regarding systems that have been bricked by the update, Sony said: "We kindly ask PS3 users to wait for further details. We will announce when ready." Meanwhile, a thread on Reddit claims that downloading a patch and restarting the PlayStation 3 in safe mode will work. The purported patch isn't available yet, however, so Sony should give more information when it's ready. We'll update as more information becomes available.