Twitter has been surveying New York's real estate landscape from an open-floored loft in Soho, trying to find the ideal office space for its New York City headquarters. Now tipsters tell the Observer's new tech site, Betabeat, that it's made its decision. The company is eschewing Soho's boutique sandwich shops and coffee houses for 340 Madison Avenue, the same building Facebook recently vacated to move a few blocks down the street. Betabeat says the deal is still a few weeks away, but considering the building was purchased for $570 million last April, the sublease is likely to be expensive. But for a company that's getting aggressive about ways to incorporate advertising, it's probably worth it to run into would-be Don Drapers in the revolving door.