Math::GSL is now using git and everyone rejoices.
I saw a fellow coworker using gitk to optimize his workflow when doing long subversion merges and also to have a more fine-grained commit history. With git, a collection of changes can be chosen and "squashed" into one subversion commit. This is useful for pushing out to a subversion repo.
This solves the problem of local modifications sitting on your machine because you do not want to push incomplete code into a subversion repo. Gitk is a simple and powerful Tk interface which allows you to search your entire commit history at many levels and shows diffs of files and lots of other metadata. It has helped me gain a larger picture of the evolution of the project.
Simply by pressing "F5", gitk updates and show you local modifications that haven't been checked in yet!