Apparently google uses a tool called Mondrian developed by the creator of python for code reviews. This inspired the development of an open source web based code review tool, rietveld and its hosted on Google code projects. Compelling reason to try Google App Engine.

"In addition, I hope it will serve as a practical tool for the Python developer community, and hopefully for other open source communities. As I've learned over the last two years at Google, where I developed a similar tool named Mondrian, proper code review habits can really improve the quality of a code base, and good tools for code review will improve developers' life."
                             -----Guido van Rossum, Python creator and Google employee

Well Rietveld is based on Google App Engine and it can be hosted only on Google Servers ( Yuck !!).

Guido van Rossum was kind enough to correct me that there is a way to port Google Apps to pure Django. For those who still think its a lot of work ReviewBoard remains an alternative.

Interestingly why does google want  you to host your code on its servers , so that its easier for them to acquire you. They already have your source code !! and you cant fool them with your buzz words.