[Samsung Galaxy Nexus] adrynalyne:
There are many questions, and they are all being answered. That said, they are spread across 34324123213132 threads. So lets create a thread where they are all asked in one place.

Q: Where do I get it?

A: The mods refused to sticky this most valuable thread for me, but you can find it here:

http://xdaforums.com/showthread.php?t=1482650

Make sure you get the right one.

Q: Where is the changelog?

A: This is not official yet. Hence, no official changelog. There is an unofficial one here by kangxi:

http://xdaforums.com/showthread.php?t=1481044

Q: Can I install the 4.0.4 OTA over 4.0.3?

A: Of course not. It only updates stock 4.0.2. That means you must return to stock 4.0.2 to flash it, or use some packaged rom from the developer forum that is at 4.0.4.

Q: I keep getting an error 7 when trying to flash. What am I doing wrong?

A: You are not stock 4.0.2 and a patch check or assert is failing. If the file it fails on is mentioned, you can replace that file with a stock version and cross your fingers. Or you can remove the patch check and installation from the installer-script in the ota zip. Of course, then you must use clockwork recovery or the likes to install. Also, make sure your recovery (if non-stock) is up to date.

Q: Do I need to be rooted to install this update?

A: Not entirely. You must be unlocked, but you can then temp boot an adb rooted kernel and place the update in /cache. When you reboot to stock recovery, you are unrooted and back to stock. That leads into how (there are a few ways).

Recommended:

Download the pre-rooted 4.0.2 kernel:
[url]http://www.box.com/s/xf6bz8f1j004bk0zc78a[/url]

Enable usb debugging
adb reboot bootloader
fastboot boot newboot.img

---once back up----
adb remount
adb push 659e0a8f24b4.signed-mysid-IMM30B-from-ICL53F.659e0a8f.zip /cache
adb reboot recovery
install from cache
choose the ota zip.
flash

Alternative method from williamthegoat:

Enable usb debugging
Put ota update on your sdcard
Temporary boot clockwork recovery. I use the one from here:
http://xdaforums.com/showthread.php?t=1428338
adb reboot bootloader
fastboot boot recoveryimagename.img (use the correct name)

---once in recovery---
Flash ota.

Note: this method contains no signature checking for the ota to verify its validity.

Q: Will this break root?

A: Yup.

Q: How do I root again after the update?

A: You need to install clockwork mod recovery.

I use the one from here:

http://xdaforums.com/showthread.php?t=1428338

Put the superuser package from here [url]http://www.box.com/s/jvcf196j7x8f8vrc9cyt[/url] into your sdcard folder.

Also grab the pre-rooted 4.0.4 kernel from here:
[url]http://www.box.com/s/dh5b2vjg13qm2uodfysk[/url]

To install clockwork (permanent) and flash Superuser:

adb reboot bootloader
fastboot boot 404boot.img

--once back up---
adb remount
adb shell
mv system/etc/install-recovery.sh system/etc/install-recovery.bak
adb reboot bootloader
fastboot flash recovery recoveryimagename.img (use the correct name)
fastboot reboot

---once back up---
adb reboot recovery
flash su.zip

To install Superuser temporarily and flash Superuser:

Put the superuser package from here [url]http://www.box.com/s/jvcf196j7x8f8vrc9cyt[/url] into your sdcard folder.
adb reboot bootloader
fastboot boot recoveryimgname.img (use the correct name)

---once in recovery---

flash su.zip

Q: I am on xxx's aosp rom? How do I update?

A: Go back to 4.0.2 stock or use one of the prepackaged, precompiled roms in the dev section. At this time, 4.0.4 is not on the aosp repos.

Q: What about GSM users?

A: I am sure they will see it soon, if not by ota, then by aosp.

More will come as I see them needing to be answered.