Android version 2.3, aka Gingerbread, has just been released to the open source repository. We are proud to offer a pre-compiled software image for the Nexus One phone. This is a snapshot of the Android "master" branch as of December 19th, 2010. The image is offered with no warranties, for the sake of early adopters who would like to flash Gingerbread, but are unable or unwilling to compile it themselves. Use the images at your own risk.
The images are intended to be flashed on unlocked Nexus One phones, using the fastboot command. The image is a zip file containing the system.img and boot.img as produced by the build tree. Flash them using the commands:
fastboot flash system system.img
fastboot flash boot boot.img
It is best to go into recovery and perform a factory wipe as well.
The zip file can be downloaded from this link.