The 10th-annual "Advertising Week" gathering looks like a big one: Digital ad spending seems to be at a turning point.
Also Monday, AOL unveiled a new system for marketers to buy all sorts of digital ads, even the highest quality ones, at massive scale through an automated system. This announcement indicates that AOL has the technical ability—plus the massive inventory—to deliver the precision of digital, with the scale of television.
The numbers bear out the trends. "Digital advertising is continuing to pull dollars from traditional media," said ComScore Chairman Gian Fulgoni, referring to the decline of ad revenue for newspaper and magazines.
"The numbers are showing that digital is growing at a rate of 15 percent, all measured media growing 3 percent, so there is a big shift within digital," he said. "The two components that are growing the fastest are mobile, up over 100 percent in the past year, and video, which is up about 30 percent."
What's driving those dramatic numbers, mobile in particular? It's partly thanks to surging Internet activity: The number of Internet usage minutes grew 86 percent from June 2010 to June 2013, with mobile activity exploding so more than half of all Internet use is now on mobile devices.
Another huge factor: Digital ads can be highly targeted and there's increasing proof that they work. On Tuesday, ComScore unveiled a study that found that people who see mobile ads are 28 percent more likely to show "purchase intent" or want to buy something than those who don't see the ads.
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The CEO of ad giant Interpublic Group, Michael Roth, said there's no question that digital is the big trend, but digital can mean so many things. One key point of appeal: data. "You can buy audiences, you can target marketing to the extreme," said Roth. "It's all about communication and messaging and if you want to tell the right story and right message and the right audience. The more data you have, the more effect you have."
Does Roth have more faith in Twitter or Facebook ads? Roth said he's interested in both, it just depends on the marketer's needs. One thing he said there's no debate about is the power and relevance of mobile.
"The consumer is watching televisions via their mobile devices at the same time. This way you can relay what's happening on their screen with their mobile device and make it more effective," he said. And the ability to sell ads both for Twitter and for the likes of CBS is a good thing for an ad agency, he added.
—By CNBC's Julia Boorstin. Follow her on Twitter: @JBoorstin.