Combine a love of social media, major league baseball and one of the longest standing professional records - Joe DiMagggio's hitting streak...oh, and the chance for $1,000,000, and you get a pretty interesting user-generated contest called "Beat the Streak"
I like this one. It has it's own dedicated portal but also linked out on Facebook (with 25,000 followers currently). Simple, straightforward and motivating. Wish me luck.
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