So this is interesting, Google just updated the product page for every Nexus 7 model on the Play Store, and the change on every one is the same: estimated battery life. Previously, the Nexus 7 was listed as having "Up to 8 hours of active use," but now the figure has been revised to 10 hours - within a day's time of the release of the Android 4.2.2 update (manual update download here).
Update 2/13/13: Google just reverted all the Nexus 7 pages back to 8 hours. Why must you toy with our feelings like that?
We've been digging for new features and changes in Android 4.2.2 (see here, here, and here), but we've yet to see anything specific about improved battery life. The timing is undoubtedly odd, though. With that in mind, to those of you with Nexus 7's on Android 4.2.2: keep an eye on your battery life over the coming days. It may be better.