A little over 24 hours ago, Google officially announced Android 4.1.2. The update was rather small, but the biggest new feature was allowing the home screen to rotate into landscape mode. Now this is something we've had in many custom ROMs and a few custom launchers already. In fact CyanogenMod's Trebuchet launcher has this as an option in the settings. Android 4.1.2 also brings some bug fixes and stability improvements, so mostly just a typical bug fix update.
Currently Android 4.1.2 is rolling out to the Nexus 7, and should be hitting the unlocked GSM version of the Galaxy Nexus soon. As for the Sprint and Verizon Galaxy Nexus well, let's not get into that. But if you don't want to wait for the update from Google, you can update to the latest CyanogenMod nightly dated 10/10 and you'll have freshly released Android 4.1.2 along with many other merges by the CM Team.
If you're already on a recent nightly of CyanogenMod, from within the last week, you should have CM Updater on your device. In which you can go to Settings, select About Phone, and select CyanogenMod Updates, then select the refresh icon to start the download of the newest nightly. Once it's downloaded just flash the newest nightly like any other ROM. Be sure to backup your information before flashing this new nightly, just in case anything goes wrong.
I've been running Android 4.1.2 from CyanogenMod 10 on my Galaxy Nexus most of the day, and it's been pretty smooth. It almost feels a bit more smoother than previous builds with Android 4.1.1, but that could be in my head. Let us know in the comments how the nightlies are working for you.