Factory images for Android 4.0.4 (IMM76I) have been made available for yakju variants of the GSM Galaxy Nexus, as well as a newcomer -- the takju build. First things first, these images are a way to return your yakju Galaxy Nexus to its factory state should you get in there and muck things all up with custom software, or for advanced users to switch from a non-yakju build to yakju. They are handy as all get-out, and have saved much bacon -- including all of us here at one time or another. You'll need fastboot up and running, and have a limited knowledge of how to flash images or read scripts. It's not hard, and if you hit a snag there's a forum full of Android lovers to help you out.
Now, about this takju thing. You might have noticed that Google decided to start selling unlocked Galaxy Nexus phones in the U.S. online today. These phones are a different model -- takju. The takju image is Android 4.0.4 (IMM76I) with some minor differences to include Google Wallet. And what's more -- flashing it to any unlocked GSM build works just fine.