$ rgit pull path/to/my/repo/
fatal: /usr/libexec/git-core/git-pull cannot be used without a working tree.
Closed because this is actually a git bug, see http://stackoverflow.com/questions/9745941/how-do-i-use-the-work-tree-option-with-git-i-keep-getting-an-error
Thanks for the report Nick!
I know there are a lot of edge cases in rgit - I even considered having it just cd to the first directory it found and run the git command there.