Sony's just pulled the 2.40 PS3 firmware update due to reports of it bricking and causing various other problems. If you're unlucky enough to already have installed it and ran into issues, Kotaku has a few solutions up. If not, just hold off until the fixed release is available soon. [Kotaku]
Update: Just confirmed it on our own PS3, which we haven't updated yet. It's not prompting us for 2.40.