The effort to put together pre-release ports of Ice Cream Sandwich just got a major boost today with a copy of the system, boot, and recovery images from a test Galaxy Nexus — courtesy of MoDaCo. It's a developer build, so it's likely to change before final release, but at least it should be fairly easy to whip up themes based on the ROM, because the apps and other files haven't been split apart by odexing. Google won't be releasing the source code for Android 4.0 until after the Galaxy Nexus launches, but for now, you can hit the source and download the entire file system.