I'm curious how folks manage their important local configurations, e.g. - is your ~/bin directory a git repo? - if you git to manage your dot files, do you use hard links or soft links?
~/src is a git repo. One script evolved into its own project and became a submodule within ~/src.
For configuration files like ~/.foobar_rc and directories such as ~/.vim/, they again are not directly version controlled but are symlinked into ~/etc which is. I don't see any reason that ~/.foobar_rc couldn't be a hardlink, but it's not in my setup.
I used to maintain a single repository at ~ that included ~/src and ~/etc as submodules, with a build script for setting up links. Always being within a git repository became cumbersome, so I moved the build tools into their respective directories (~/src and ~/etc) and now clone and build each repository manually.
Lastly, since private repos aren't (weren't?) free, those submodule repos are really just branches of the same repo that share no common ancestors.