The numbers are in and show that U.S. adults now spend an average of 2 hours and 51 minutes on their mobile devices each day. What are marketers doing about it? Adapting. As eMarketer reports, mobile ad spending will increase by a whopping 50% this year to nearly $29 billion. And by 2016, it's predicted that of all digital advertising, spending related to mobile advertising will exceed desktop for the first time. What types of mobile ads are we most likely to see popping up on our screens? For now, display ads (things like banners, sponsorships and rich media) and search ads are expected to be the biggies. The concept is nothing new. Just as social media created a major shift in digital marketing, mobile is on the verge of doing so, too.