Tomas Restrepo wrote a post about
sharing dotfiles between Windows and Ubuntu,
specifically about sharing .vimrc (Linux) and _vimrc (Windows)
and the .vim (Linux) and vimfiles (Windows) directories.
I have a different solution.
On Windows, my C:\AutoExec.bat includes:
%HOME% (C:\gvr) contains _vimrc, vimfiles,
and other stuff accumulated over many years.
This directory is stored in a personal Subversion repository at DevjaVu.
All my Vim files are stored with Unix LF endings, not Windows CR-LFs,
so that they'll work on my Mac OS X and Linux boxen.
I play some games with if has("win32") and
if has('gui_macvim') to ensure that my _vimrc
On my *nix boxes, the gvr folder lives under my home directory at ~/gvr,
and ~/.vimrc and ~/.vim are symlinks:
$ ln -s ~/gvr/_vimrc ~/.vimrc
$ ln -s ~/gvr/vimfiles/ ~/.vim
In addition, the dotfiles that I keep in SVN are stored locally in
~/gvr/dotfiles without a leading period in their names,
which makes them easy to see:
$ ln -s ~/gvr/dotfiles/bashrc ~/.bashrc
This arrangement works well for me.