Used to think this is a great idea. But reality told me this could lead to chaos (way to much chaos), especially when the company is going through a finanancial crisis (hopefully not the case for FB for a really really long time). For most of the companies, leadership should be vital. Things like hackathons are luxury game rich people allow to play.

I was thinking more that you let your employees come up with new ideas every once in a while. Like Google 20% time or LinkedIn HackDays.