It's completely changed my approach to open source software. Before GitHub, open sourcing something was a bit of a drag - you were committing yourself to setting up a mailing list, accepting patches etc - the administrative overhead was enough to put me off releasing a lot of my code.

GitHub is ideal for the "fire and forget" method of open source. I can knock out a bit of code that might be useful to someone, throw it up there and forget about it. If someone likes it and wants to improve it they can go ahead and fork it without me ever having to think about it again. If I /do/ want to maintain it, it's really easy to keep track of the modifications people make and merge them back in to my version.

The amount of high quality code coming out of GitHub projects these days is astounding, and I'm willing to bet a LOT of it wouldn't ever have been released using the older systems like Sourceforge and Google code.