Today, at the Web 2.0 Summit, Twitter's CEO Dick Costolo confirmed that the micro-blogging-turned-news platform is now valued at $8 billion. He went on to add that the company recently raised $800 million in two rounds of funding. Twitter's official valuation has lately been rumored to be around $8 billion. Many said that was impossible because, welll, how the hell could a company that brings in less than $200 million a year without a solid, proven revenue model be worth that much money? We have a few ideas...