PS3 Firmware 3.56 is reportedly causing HDD problems for a number users. Just like that one time. Oh, and that other time. One day, Sony might release a Firmware update that stops its Firmware updates from being shit.
The issue seems to be the same as usual, with users on multiple forums complaining that they cannot update their hard disk drives since installing the update. This seems to mostly be affecting more recent PS3 units, although some older ones have been fallen foul of the chicanery as well.
As usual, you can expect Sony to release some sort of fix for afflicted users in due time.
After releasing roughly ten billion Firmware updates, you'd think Sony would have actually gotten good at them.