I just used Git for the first time and I think I finally understand what all the hullabaloo is about. Git is a distributed source control tool being used by the Linux and Ruby on Rails community.
The difference between Git and other source control systems like Subversion is that there is no need for a central repository for your source code. Your code remains completely distributed amongst the various machines and people that are working on it.
I currently use Subversion to maintain my source code, but I am thinking that I may like Git better.
UPDATE: To install Git on Mac OSX (10.5) I used the following, graciously taken from this forum post at Slicehost.
First, get the source code for the latest stable build here, then:
sudo apt-get build-dep git-core
tar xjf git-1.5.5.1.tar.bz2
cd git-1.5.5.1/
./configure
make
sudo make install