It’s a mobile, social and visual media world and marketers better adapt or risk losing customers and sales. Of all the takeaways at Media Kitchen’s Digital Media Venture Capital Conference in New York Thursday, that one seemed paramount.Business Insider CEO Henry Blodget noted that for the first time in 30-plus years, the PC market is now shrinking. “That’s a profound change,” he told conference attendees. Mobile usage is soaring and “cannibalizing everybody,” referring to other media channels.That said, Blodget said it would be an “exaggeration” to declare the death of TV, as so many pundits have in the past. No doubt it’s being “squeezed” he said. But for the foreseeable future, it will be a multiscreen world that includes TV, PCs, smartphones and tablets and probably a few others like the wearable computers Google Glass and Apple’s much anticipated iWatch. “Second screen is a big opportunity,” Blodget said, noting that more 80% of young TV viewers (ages 18 to 24) simultaneously use a phone or tablet while watching the big screen.In the e-commerce space, “mobile commerce is a super big deal,” asserted First Round Capital Partner Chris Fralic. In the fourth quarter of 2012, he said, 13% of all e-commerce was mobile commerce. Transactions on eBay conducted via mobile now total about $13 billion or around 17% of the company’s gross merchandise value, he said. Marketers can’t afford to ignore Twitter’s commerce channel, said Fralic, noting a recent deal between the social site and Starcom MediaVest Group, that he estimated was worth about $400 million.Nikhil Sethi, the CEO and co-founder of social marketing company Adaptly, said the social space has transformed the notion of consumer identity for marketers. For years in the online sector, marketers relied on cookies to identify and track potential customers, he said, describing the approach as a “hacked structure.”Now, he said, consumers are telling marketers “exactly who they are” through social networks like Facebook and Twitter. Send a friend a note through Facebook that you’re staying home from work due to a cold and you’re likely to receive an ad for Kleenex, he said.