SAN FRANCISCO — For anyone with a crazy idea for a Web business, the way to make it pay was once obvious: get a lot of visitors and sell ads. Since 2004, venture investors have put $5.1 billion into 828 Web start-up companies, and most of them are supported by ads, according to the National Venture Capital Association........http://www.nytimes.com/2009/05/25/te....html?_r=1&hpw