The response to the initial public offering last week of shares in LinkedIn, the business social networking company, was euphoric, with the market capitalisation on the first day approaching 40 times revenues. Yet this was modest compared with the earlier IPO of Renren, China’s biggest social networking company, where the initial valuation was closer to 100 times revenues. In the secondary market, meantime, shares of Facebook and its ilk sell on equally fanciful multiples. As in the dotcom boom investors have fallen victim to long-termism, a disease that can be quite as damaging as short-termism to efficient capital allocation – though very good for investment bank pr