Online collaboration: What, to you, has been the most useful thing about using Online SVN?

I love Github. It is my portfolio. I have used it to collaborate both privately and publicly on online projects. It is a great for SCM. It is an incredible reference library with thousands of users. It is a showcase. A place for code snippet storage.

Recently, someone suggested in an interview that it is a great way to learn: to fork code on github; to contribute on open source projects, etc. I have done this before, but only really on invitation... And I am not sure about just going to someone's project and submitting stuff - except of course if they made an open invitation... How do you feel about online collaboration, and what do you think is the best way to go about it? Have you come across some nice sites that invite this type of collaboration? (Also apparently "SVN" might not be 100% correct way to refer to it?)