So LinkedIn is raising additional financing at an extraordinary valuation of $250m, according to a senior exec at the business networking site. The planned round, of $13m, seems at once too much and too little. I'm not quite sure why the Sequoia portfolio company needs more external funding if, as Keith Rabois, the exec, told Bambi Francisco, LinkedIn truly turned profitable in March this year. And, if the company's seeking to build up a hoard of cash while investors are ravenous for social networks, why not raise more?