Getting consumers to use mobile devices as a second screen while watching television has been a lot easier than marrying mobile activity to actual shopping transactions, writes Lauren Johnson. GetGlue CEO Alex Iskold says that scale remains a problem for three mobile-shopping models, where mobile is used for buying what's advertised on TV, where consumers buy products featured in shows, and where they buy products related to show content. "It takes a compelling value proposition to shift TV viewers from passive TV watching into taking action -- overcoming the inertia of leaning back and doing nothing," says David Jones, Shazam's executive vice president of marketing.