I just bought a new Mac with OS X Lion and I checked in the Terminal what version of git is installed by default. I got the answer
git --version
> git ver
The latest version was not available as a binary for mac on git-scm.com, so I installed from source. I was missing a required package for localization, and added NO_GETTEXT=true to install without localization.
git clone https://github.com/git/git.git
cd git
make NO_GETTEXT=true
make NO_GETTEXT=true install
This installed git under ~/bin which I then had to add to the beginning of my PATH variable.