Burton Group Catalyst conference opens in San Diego, tackling cloud computing, virtualization, security and many other topics. Tech start-ups should rent virtual servers from Amazon Elastic Compute Cloud, expert John Seely Brown says. Start-ups that take in large sums of money from angel investors are giving away a large portion of their future value, he says. Some of the new cloud computing technologies may help restore lost profitability, Brown said, arguing that “cloud is much more disruptive than any of us have ever thought””]