When you've got a passionate community of readers like Tricycle does, you have to tread carefully when it comes to changing your revenue model.  We spoke with editor and publisher James Shaheen recently about Tricycle's decision in 2008 to switch to an online membership model and how it not only slashed the nonprofit's fundraising burden, but also led to a $200,000 revenue surplus last year. Read on to discover how the site is getting a 10% free-to-paid conversion rate, an 80% retention rate, us...