I spent part of the weekend playing with gitosis, a tool for administering remotely-accessible git repositories.
Access revolves around ssh and public/private key pairs. You give me your public key, and I can grant you selective permissions, repo-by-repo, if I'm the gitosis administrator. Once I do, it's painless to check stuff in and out, since all the permissions stuff is under-the-covers. Much nicer than Subversion's cacheing of passwords in plain text.
One of the coolest things is that the administrative data, including public keys, are kept in a git database. If I'm the (or an) administrator, I can administer access remotely, with git pull and git push -- including adding new users and their keys -- using gitosis itself for the repo access.