Just today, Google announced that it was rolling out Android 4.0.4 to the Android Open Source Project (AOSP) for download, with build IMM76D. The note at that point by JBQ was that the timeline for ROM push for the final build was unknown. 

In a tweet and Google+ post, Google has now noted that Android 4.0.4 images are beginning to push out for the GSM/UMTS Galaxy Nexus and Nexus S, and Xoom WiFi. Absent are the CDMA/WiMAX Nexus S on Sprint and the CDMA/LTE Galaxy Nexus on Verizon, both of which are likely waiting on carrier approval. The update includes bugfixes, stability improvements, faster camera launch (which we've noticed in leaked 4.0.4 builds), and better performance in some areas.

We’ve started rolling out Android 4.0.4, Ice Cream Sandwich, to UMTS/GSM Nexus S, Xoom Wi-Fi, and HSPA+ Galaxy Nexus devices. #android

— Android (@Android) March 28, 2012

We're anxiously waiting for our own GSM/UMTS Galaxy Nexus to get the push so we can test out the final build and see what all has changed. Hopefully Google also updates the factory images for Galaxy Nexus pages for those of us who are impatient. 

Source: Google