I have started my transition from SVN to Git. It is an open source distributed version control system whose design allows fast and easy branching and merging.
Have you experience with SVN merging a 2 million lines code 6 months after the branching because of the development of a major feature that simply broke the software for 3 months before getting something working? Well... I experience it... twice! The time, it took me a week of pain and probably some consequences of this merge still remains (3 years later!). The second time, I thought about suicide before the merge to find a way out!
For years, SVN has a new feature for about each new version "branching and merging is now done right!". Well, it never happened and it won't happen because, conceptually, SVN is just wrong.
This is from where is coming from my motivation to use Git. With Git, I expect to use a version control system that works and that allows me to manage my projects with a real development model driven by the version control system. A merge takes about 1 second with Git... which gives a complete different perception of branching!
Beyond that, it's so far just full happiness!