As of, oh, right now, there should be a prompt on your PS3 asking you to upgrade to 4.45. Whatever you do, don't accept it. Not yet, anyway.
We've started getting reports from readers that the update is bricking their system, locking their consoles on the boot-up "ribbon" screen, and a thread on Sony's official forums shows the issue is far from isolated.
It's obviously not locking up everyone's console, but there are enough already affected that you won't want to roll the dice.
Problem after update to 4.45 [Sony, thanks everyone who sent this in. Sorry about your PS3s :( ]