At the same time, the shift from PC-based display ads to mobile audio ads is driving down the blended CPM.

FORBES: Connect

But its overall share will decline as marketers shift search spend into biddable display investments, mobile marketing, and even social media.

FORBES: Interactive Marketing Spend Will Near $77 Billion By 2016

This discovery will shift away from retail websites and display advertising and will happen more and more on tablet apps and curated feeds on social networks.

FORBES: D-Commerce And The Pixel Web: The Future Of E-tailing