Sony Computer Entertainment just made system software update 4.75 for the PS3 available for download via PSN.

The patch can also be downloaded via web here for the North American version and here for the European version.

At the moment no patch notes have been released, but at first sight no large changes have been introduced to the system.

Update: the official Japanese website finally listed the update and its changelog, which is what many of you probably imagined:

"the stability of the operation of the system software has been improved."