In my opinion, one of the stickiest features (and one that increases engagement) with Facebook is photo posting and tagging. Being so compelling to users, improvements on the photo taking and photo tagging experience are explosive features for users. And so they are potentially big fish for existing social networks (who want to maintain their engagement with users) and to others who want to increase their social capabilities and social cool. To follow the logic through, the sum of being compelling to users and potential acquirers means a compelling opportunity for entrepreneurs. Consistent with this thesis is Instagram’s amazing reported growth and the rumored $100 million offer for Path by Google.