Earlier this morning the folks from Google started pushing out a quick update to Android 4.2.1 Jelly Bean. The update was initially only rolling out to the LG Nexus 4 and the Nexus 10, but now the Nexus 7 can also enjoy the latest and greatest from Google. Now we're just waiting for the same update to arrive for the HSPA+ Galaxy Nexus, which should be any time now.
The update is extremely minor going to Android 4.2.1 Jelly Bean, and is mainly just fixing a few found bugs with Bluetooth, WiFi, and of course that ridiculous "missing December" problem. Basically Google forgot December in their people app (not Calendar) and some people couldn't insert birthdays and such. Pretty minor oversight causing a big problem.
So now we're here with 4.2.1 which is rolling out as we speak. Google just pushed 4.2.1 to AOSP for everyone to sync and download, and now the Nexus 7 is getting the same treatment as those other Nexi are. The update should just arrive within the next 24 hours or so for all Nexus 7 users, so don't worry about missing December in just a few short days.
As usual, you can select to check for updates manually, try a few of the clear Google Services Framework data in settings "tricks" or just download it directly from Google. You'll need to download the file below if you chose that route, install it with a custom recovery, or use the stock recovery and push it through ADB as usual. A custom recovery is always easiest for this procedure. Or just wait for the OTA notification as the update should be appearing on your tablet any minute now. Enjoy that freshly baked Jelly Bean!
Download: Android 4.2.1 Nexus 7