A recent firmware update spelled trouble for some PlayStation 3 owners, crashing their consoles. Sony apologized and, as promised, has released a 4.46 patch, as well as offering details on how to implement it if you were one of the affected users.
If your console hasn't been displaying the XMB since the update, a step-by-step guide is available. In short, it involves creating a few folders on a USB flash drive with at least 168 MB of free space. You'll then download the 4.46 update to the stick, and start your PS3 in Safe Mode. After that, you can plug in the flash drive and apply the update to get the system back in working order.
Of course, version 4.46 is available for all users, and most can simply download it as usual. The update seems squarely focused on fixing the 4.45 bug, so if your system is already running fine you won't see new functionality coming out of the update.