We use an often ignored feature of git branches where we include "/" characters to show a hierarchy, such as "origin/releases/2011/5". The git plugin supports this well overall, except for the GIT_BRANCH token macro, which if you don't specify fullName reduces it to "5" instead of "releases/2011/5". The GIT_BRANCH token macro should strip off the repository name only and not everything before the last slash.

Below is where the full git ref spec is documented.
http://www.kernel.org/pub/software/scm/git/docs/git-check-ref-format.html