Amazon has released the Kindle Fire source code as per the open source licensing agreements. While the source code is of no use to normal users and it is very important for developers looking to build custom firmwares for Kindle Fire and other tinkering around the device and even using the code in other developments.
Interestingly, Amazon had released the source code on November 14 itself, a day before Kindle Fire became officially available. Nice work Amazon..
This release will surely boost the ongoing development by Android dev community for Kindle Fire. You can grab the whole download from here. On the other hand, Google has been fast enough to give access to ICS source as well recently, which would surely be leading a few ICE based custom ROMs for the device pretty soon.