As expected the update is bring rolled-out OTA, and will soon reach everyone. The ICS running Galaxy Nexus are getting a 147MB upgrade, while Android 4.1 running devices will get a smaller 8.50MB update.
On the other hand, even though there is still sometime in Nexus 7 to reach retail market, Google has pushed Android 4.1.1 for the tablet as well. The tablet is currently owned by the select Google I/O attendees. The update size for Nexus 7 is 12.6 MB and is also being released over-the-air.
You can manually download the updates from here and apply them using the detailed guide given at XDA.
For Galaxy Nexus:
takju-JRO03C-from-JRN84D (8,914,753 bytes)
takju-JRO03C-from-IMM76I (154,343,776 bytes)