Bloomberg recently highlighted how skepticism is building for digital ads on platforms like Facebook and Google due to ad fraud, high costs and limited attention spans:

Digital advertising's longstanding problems aren't improving. Newly published research by a group of marketing firms found nearly 20 percent of digital ads were bogus -- that is, not seen by humans, or deliberately invisible on websites and apps. That's a lot of wasted ad spending. Again, bogus ads are a perennial problem, but they've been tolerated for too long.

Marketing firm Adobe said this week that the costs of digital advertising were growing more quickly than the cost of TV ads and that the growth in spending on web search ads wasn't resulting in a commensurate increase in visits to the advertisers' websites. That echoes the disillusionment expressed by an executive at Procter & Gamble -- the world's biggest buyer of advertisements --who said big companies weren't seeing fast enough sales growth to justify the $500 billion spent annually on ads.