It's probably now worth thinking about Facebook more as a giant advertising VC house more than as 'Facebook.com'.

Facebook's main asset is its social graph and cross device map, which only Google currently has anything comparable too.

Any time a new type of app, ad unit or social trend becomes popular (group chat replacing FB groups for instance), they will buy it before it gets traction. Instagram has a much nicer ad unit format than Facebook, and appeals to a more upscale audience.