The update has been confirmed for Samsung Galaxy Nexus yakju models, which are those not sold directly by Google. The good folks over at XDA have even posted the update.zip so you can manually flash the update if you haven't received it yet. There are also unconfirmed reports that the update is pushing out to the Nexus 7 and Nexus 10.
The update is assumed to be a security update, and the actual features and changes are unconfirmed as well. If your Nexus is running JWR66Y, let us know in the comments, or send us a screenshot of your about page, along with your device and location.