Love this post. Monetization on mobile, as shown by Facebook's struggle to do well, is the next code to crack. I agree that as users are on mobile in a very focused state of mind, they are not open to advertisements, in particular not those that are in the way of achieving a goal. Subscription, in-app purchase might be better, also when users become more aware of the fact that if they are using a free service, they themselves are part of the offering being sold to the companies paying the bill.