The release of firmware 2.40 earlier today seems to have caused a wide number of issues for those who updated their PlayStation 3 consoles. Shortly after going live, reports began to emerge on forums about issues such as console freezes or even console bricking - in which case reformatting the hard drive is the only solution.
There doesn't seem to be any real pattern as to which systems are affected either, with pretty much every PS3 model being reported as troubled by the issue. A representative for the company quickly emitted a statement, saying they were "looking into the matter," and as of this writing they seem to have pulled the update from its servers. Even when the firmware is back online, though, you should probably head to the official Sony PlayStation boards and see if other issues arise before deciding to update to 2.40.