Mobile App install ads are 30% of mobile ad revenue:

The mobile app-install ad — an ad unit that directs users to download a mobile app – is closely identified with Facebook, the largest social network. But these ads have become so lucrative — driving one-third of all mobile ad revenue — that virtually every other internet property has created their own version. 

Mobile app-install advertising is already found on Twitter, YouTube, and mobile ad networks like Millennial Media. Pinterest opened the door to the ad format recently  with "app pins," and no online publisher wants to be left out of the rush. 

New and exclusive data from BI Intelligence finds that US mobile app-install ad revenue will top $4.6 billion this year and grow to $6.8 billion by the end of 2019, increasing by a compound annual growth rate of 14% from 2014. We believe mobile app install ads accounted for about 30% of mobile ad revenue last year.

Wow. A third of all mobile ad revenue for mobile app install ads feels like it's just getting started.