I'm really impressed with this -- I would love to see this see functionality for other VCSes (subversion, etc) so that I could use it with my non-git projects. The vimscript looks pretty clean -- maybe I have a new weekend project ahead of me.
Thank you! I wasn't aware that these plugins existed already. While I was getting excited to get my "vim -D" on to get the script in the OP to work with svn, I might just work one of these plugins into my workflow.
edit: just a quick hack for a "vim svn gutter": https://github.com/prg318/vim-gitgutter
The code is really clean and it would be fairly trivial to adopt this for use with any other VCS. Open source yay!