Home-improvement rating site Angie’s List was founded roughly two decades ago. More than two million U.S. households are using the service to gain information about the quality of 700-plus services (plumbing, electrical work, and so forth) provided by local companies. Angie’s List members submit reviews at the rate of over 60,000 per month. The firm’s success is suggested by the fact that it generates roughly $220 million in annual revenue.