Not really. Advertising as a way of monetization might be easy to understand, but harder to actually implement and sustain. It is not like 'just put ads on it',

Not really. Advertising as a way of monetization might be easy to understand, but harder to actually implement and sustain. It is not like 'just put ads on it', then money will flow by itself. It will take some non-trivial efforts for Pinterest to actually make their model working. The competition is out there: Facebook has one of the biggest and richest demographic data in the world, and it could easily leverage that to drive sales on Instagram, make it more appealing to advertisers, which I think Pinterest should be afraid of.