It's not the rats you need to worry about

If you want to know if a ship is going to sink, watch what the richest passengers do.

iTunes and file sharing killed Tower Records. The key symptom: the best customers switched. Of course people who were buying 200 records a year would switch. They had the most incentive. The alternatives were cheaper and faster mostly for the heavy users.

Amazon and the Kindle have killed the bookstore. Why? Because people who buy 100 or 300 books a year are gone forever. The typical American buys just one...