Facebook contributes to the open-source community ?

While Facebook opened its API long ago to developers so they could build applications on top of its product, the site is far from open-source. Advocates of the standard would cut your tongue out for saying so. The social network was built entirely using open-source software, but don’t go confusing that for its current status. What it has done is contribute to the open-source community by devoting some serious man power to the development and application of PHP, OAuth, HipHop (a system that translates PHP to C++), XHP, and HTML5 – and it releases bits and pieces of its infrastructure along the way, which is more than a lot of proprietary systems can say.

http://www.digitaltrends.com/computi...ode-this-year/

It does actually. We even used HipHop PHP for one Pressflow project.

It worked fine ?
Was it for php existing project or you created php project to transform it into c++ later ?

They also mirror a few distros and other items via their .net domain ->
http://mirror.facebook.net/