It looks like that latest OS 184.108.40.206 leak for the BlackBerry Bold 9790 held more than just marginal updates to native apps. They also threw in a new feature called “Battery Saving Mode” in the menu spotted by N4BB. The new option lets you choose if and at what threshold the OS should kick into Power Saving Mode to adjust your settings to maximize remaining power. I am convinced BlackBerrys have been doing some of this stuff for awhile but have not exposed the options to users when it comes to doing things like turning off the radio at 5% battery.
Kevin @CrackBerry also managed to score a video of it running on a Bold 9900 at DevCon Europe: