git submodule is an interesting way to maintain upstream repositories. Kind of similar to what I have been doing with svn repositories inside a main git repo.
In our git repo, we create a .gitmodules file and declare:
[submodule "local path to where our git sub-repository should exist"] path = local path to where our git sub-repository should exist url = git://remote path to our upstream git sub-repository
We can then grab the latest and greatest from this upstream git sub-repository by calling:
git submodule update --init
Nice little trick to maintain modular code and use them for various projects as required.