Building a new HQ is largely an exercise in vanity and boasting. There is almost always an existing building that would serve just fine, otherwise.
"The largest open floor plan in the world"? Oy. I hope they hire some good acoustics folks before they finish the planning stages.
Atari, Apple, Sun, Cisco . . . these companies all had significant hard times about the time they started large new sets of buildings.
I think it may be worth it, a big part of hiring the best talent now is creating an environment that they enjoy rather than dread being in. Not that the open plan office is for everyone.
Am I being dumb or are you saying Facebook pays for their employees' groceries if they choose to work from home instead of working at the office and eating at the free cafe(s) there? I'm impressed if so (even though it probably wouldn't really add up to that much money for a company that can afford to pay $1B for Instagram).