We ordered one as well, and I've been futzing with it
http://www.androidcentral.com/samsung-galaxy-nexus-oem-desktop-dock-review
Here's what I've learned:
Stock 4.0.2 DOES have the kernel drivers that trigger docking, but does not have the spot in the settings for Dock. I use a GSM nexus, and didn't have trouble going into "Car Mode", but the only thing Car Mode does is turn the screen sideways

The phones speaker doesn't work while docked, nor does the mic.
I built AOSP 4.0.3r1 last night and flashed it, and the dock works as expected every time -- goes into deskclock mode, all buttons work, and all sound works, both from the phone speaker and from the external speaker jack. BT always worked FYI. Phone calls are automatically put into speakerphone, and the alarm works just fine.
short version -- 4.0.2 doesn't have all the software for dock operation. AOSP 4.0.3 does. I'll assume the 4.0.4 leak does, too. Welcome to the joy of having a Nexus, and being the final beta tester for Android
Because I'm a total basement nerd, I got some thin wire and a multimeter out. If anyone wants to make their own Pogo pin dock:
Top pogo pin (closest to the power button) is + voltage
Bottom pin is ground
Center pin is digital signal used for audio