We've used CVS, SVN over the years and are now using Git. If you've not a programmer you probably wouldn't be familiar with tools like Concurrent Versions System or Subversion which allow for precise sharing & collaboration between thousands of people but with over 150,000 lines of code in Drupal Core, you really need to have a way to manage these details to ensure that you've got the highest quality control possible.  Git is the latest in social coding and because if it's distributed framework it should allow many more people to evaluate, experiment & collaborate with the Drupal community.  

Git & Drupal

Knowing that Drupal was adopting Git, we made the move to adopt it, replacing many of our other repositories.  There is quite a learning curve to get it set up and integrated with our processes, but it's been very impressive thus far.  Our ability to quickly integrate around a standard tool set that allows us to both track & centralize changes for our projects is already beginning to pay off.  Configuration files, default error messages, custom modules, client themes, not to mention Drupal core and community contributed themes/modules.