The first devices to get the 4.2.1 update that fixes the December missing from calendar and some other minor issues were the Nexus 4, 7 and 10 just a few days ago. Today it seems that Galaxy Nexus was next on the list because Google started releasing the OTA.
The update is available for both Android 4.2 versions takju and yakju. The update however is a very minor one, and except fixing the December issue we are not yet sure what other issues it fixes. There are a lot of issues with Android 4.2 for Galaxy Nexus
and it doesn't seem Google has fixed any of them yet. However it is a good thing they released this update also.
The update should come to all devices soon. If you didn't receive the update you should wait until you are prompted with the OTA update on your screen.
are some of the features in Android 4.2 that you might be interested in.