As of the time of writing this post, there has been no official statement from Google, but unofficial reports suggest that this update fixes signal issues experienced by many GSM Galaxy Nexi after the IMM76D 4.0.4 update.
The update seems to be minor. Download the OTA update zip here:
This update zip works ONLY ON STOCK IMM76D 4.0.4 ROM WITH STOCK KERNEL. That means, ALL files in your system and boot partitions should be unmodified (file additions are okay, like with the case of root). A custom radio and/or root is fine for this update, though. Instructions on how to flash the zip, are on efrant's awesome thread here:
As of now, it's likely that the update is only for GSM Galaxy Nexus models running the Yakju build. Since the signal issue affected GSM models only, it's likely that the CDMA Galaxy Nexus won't get this update.
Time to start spamming the "Check Now" button even though I didn't have the issue in the first place!