Over the course of the past day, we have seen Google start to rollout an Android update, first to Nexus 10 devices, then to Nexus 4 devices, and most recently to Nexus 7 devices. The OTA update to version 4.2.1 is probably still in the process of propagating to all device owners. In the meantime, the source code has landed in the Android Open Source Project according to Technical Lead Jean-Baptiste M. Queru. Factory images for devices are expected to be available in a few days according to Queru.
The update is small, but packs an important fix in correcting the missing month of December. According to sources, the update also includes support for HID gamepad/joystick devices and some improvements to handling of vibration notifications.
source: Android Building Google Group