After putting Dilbert online for free, Scott Adams reported, "Free is more complicated than you think."In this talk, Tim O'Reilly does the math: just how many page views do you need to support an e-book with advertising? How popular does your blog need to be? What percentage of customers who sample a free product end up paying for more? Which online business models produce revenue comparable to existing print models? How much will others need to grow to fill the gap?Free is a strategy, not an endpoint. It's time to stop wishful thinking and build business models that work.