New York's financial media are obsessed with Silicon Valley as Facebook — with 900 million subscribers — prepares an initial public offering that could set records on Wall Street. There's no clear evidence that advertising on social media really works, but everybody has got to be there. So Facebook might be worth $100 billion. On the other hand, Goldman Sachs and other Facebook insiders will cash in early, and small investors are being warned that the price might be too high. General Motors stopped paid advertising on Facebook. Smart move or evidence that the old bricks-and-mortar economy just doesn't get the Internet Age? However it shakes out, Facebook's IPO is a media event big enough to create a cultural moment.