Japanese site emuonpsp reported today that a combination of keys was found in the settings menu to display some hidden information about the firmware installed on your Playstation vita.
This menu contains information about the system build, repository, revision,Ö doesnít look like itís super useful information for now, but still interesting I guess.

The combination to get this menu to show requires practice but I could confirm it works on my vita (Firmware 1.510).

1.Go to Settings > System > System Information
2.Press simultaneously RTrigger + LTrigger + DPad Left + Square for a few seconds
3.Release those buttons then immediately press the start button
4.tadaa, additional information shows up