Installation

git clone git://github.com/jasongrimes/dotvim.git ~/.vim

Create symlinks:

ln -s ~/.vim/vimrc ~/.vimrc

Switch to the ~/.vim directory, and fetch submodules:

cd ~/.vim
git submodule init
git submodule update

Managing plugins

Add a plugin:

cd ~/.vim
git submodule add http://github.com/tpope/vim-fugitive.git bundle/fugitive 
git add .
git commit -m 'Install fugitive plugin as a submodule.'
git push

Upgrade a plugin:

cd ~/.vim/bundle/fugitive
git pull origin master

Upgrading all bundled plugins:

git submodule foreach git pull origin master

Credit

Approach taken from this vimcast by Drew Neil (aka nelstrom).