This week's Subscription Site Insider Case Study features the Mad Mariner, a site visited by more than 70,000 unique boating enthusiasts each month. One of the lessons we learned from site publisher Glen Justice was that you have to test different types of interactive content to find exactly what will engage and inspire your audience. Magazine sites often throw up a message board or add commenting capability to their articles and assume that's all it will take to turn passive readers into engage...