What do you do if you land the biggest software-only investment round ever? You build some nice office space for your team, that's for sure!
Business Insider has a nice photo-essay of the GitHub office space here
It looks like a fun place to work, although I sure don't understand this new-fangled passion for everybody hanging out in one big room together.
I worked in an environment like that once. It was noisy, distracting, and unproductive, and after a few months many of the individual engineers had worked around the problems either by changing their office hours so they weren't in the shared space when others were, or by stacking books and papers on their desks to build miniature walls for privacy and less distraction from co-workers.
Oh, well, I guess I'm a dinosaur :)