Google seems to have started rolling out Android 4.2.1 update on some Nexus devices.
This update fixes the bug in the People app that had December missing from the date field. This bug was in the official Android 4.2 build for Nexus branded devices.
Google has not officially talked about any other changes in this build.
Reports say that it Nexus 4 and Nexus 10 devices are getting it right now. Galaxy Nexus and Nexus 7 are the two other devices which got the Android 4.2 build officially from the company.