27.) If you're not paying for it, you're the product.

We all want stuff for free, but we rarely stop to consider what the hidden costs attach to the things we consider free. Costs like privacy and peace of mind. I lifted this rule from a discussion on MetaFilter on the overhaul of the social aggregation news site Digg last year. The site's redesign had very little to do with improving the user experience and a whole lot to do with positioning users to see content they're intended to see.