I use git for version control even on small / one guy projects and it has saved my bacon more times than I can count.
Public / open source projects all go up on github for (free) backup and distribution at the same time. It's easy to back up private projects to private web space. Couldn't be simpler.http://git-scm.comhttp://github.com
The Arduino team is using github in a very transparent and open way to develop, track issues, and document the core. So there are other reasons for people who hang out here to be on github as well.