Great advice. Read the whole thing!
As I look across the landscape of online content, I have observed some things that clearly work:
1. Users don't care where the information comes from. They just want to know what is out there. So failing to include the free Web with your paid service is a big mistake.
2. Failing to provide premium for pay information on your free search is just as big a mistake. If the answer to a question relates to health or wealth, people will pay.
3. You have to be very clear and honest with users about what is free and what is paid. Don't try to charge for content that is free elsewhere.