"How much is buzz and a big online user base worth?"  That's the question a lot of people have been asking after, in what's the biggest tech-related financial story in a while, the company called Twitter was reportedly valued at $1 billion in a round of funding last week. What's more (or technically, less), the $1 billion isn't all theoretical.  Twitter is supposed to have raised $100 million from a group of investors including the respected mutual fund specialist T. Rowe ...