Unwinding the Free Business Model

We’re currently moving through a period of disequilibrium. The prevailing price structures and ways of doing things are unlikely to be viable in the long term. As more eyeballs move to internet connected devices, the supply of advertising inventory is going to grow explosively and it is going to become cheaper and cheaper for advertisers to reach massive audiences or just the right audiences. But as advertising fees decline, web publishers are going to have to find other revenue streams to survive.

via David Evans on Catalyst Code

Although the article takes a closer look at the publishing industry, the same is true for web start-ups relying on advertising as their only business model. What is the 'mixed model' (free + premium content in the publishing space) for your idea?