The system will be updated to play nice with the Vita, allowing you to use the system for content management and backup.
It's been a while since we've had an even numbered update to the PS3, which means that we're in for a big one. The primary features coming to the PS3 in the latest update are, as you might expect, related to the upcoming PlayStation Vita.
Patch 4.0 will let your PS3 act as a storage device of sorts for the Vita. You'll be able to transfer movies, games and even update software on the Vita using the PS3. You can back up saves too, which is essential, as anyone whose lost a memory card in the past will tell you.
The update also give PlayStation Plus members the ability to enable or disable automatic updates on games, system software, recommended titles and trophy information.
Of course, those are only the pre-patch notes. Once everything is up and running, Sony will release a full list of what's new and what was changed.
Source: PlayStation Blog