Campaign supporters fork over millions of dollars on rewards-based crowdfunding sites in exchange for goodwill, a trivial reward like a T-shirt or, some say, nothing more than an empty promise. The crowdfunding sector grew to $2.7 billion in 2012—financing more than 1 million campaigns globally, according to an annual report on crowdfunding from Massolution. That figure is expected to rise 81 percent to $5.1 billion in 2013.

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