GitHub still has the best UI for code hosting I've ever seen, and continues to improve their user experience in little bits throughout the year. The fact that open-source projects by and large have moved to GitHub now that SourceForge and Google Code are no longer reliable hosting options was probably the final nail in the coffin, although GitHub has been the major player in open-source code hosting for years in my opinion. But, you're probably correct in some way in saying that it's a "facebook for programmers"...it's relied on by companies to make hiring decisions, developers to find out what each other is up to, and projects to host their resources. GitHub is a great mixture between social media, infrastructure, and general workflow or development tools, and I think that's what has made it so valuable.

I can't think of a better place to host my code.