No pressure, Mark Zuckerberg! Wall Street insiders are closely tracking the nation’s biggest Web IPO offering ever—Facebook—making sure things go well on day one of its trading. The third-biggest IPO was made official Thursday when the company announced it had raised $16 billion in funding to seek a $38 share price, giving the Silicon Valley leader a $104 billion valuation. "It has to go off without a hitch. There's going to be a lot of visibility on this," said Larry Tabb, CEO of a consulting and research firm. "If this goes poorly, it will not just be a poor reflection on NASDAQ—it will be a poor reflection on the U.S. market structure." Facebook shares are scheduled to begin trading at 11 a.m. EST, 90 minutes after the stock exchange opens, giving brokerage firms enough time to process what is anticipated to be an enormous amount of opening-day orders.