Michael Wolff at Technology Review seems to think so, as he explains in a well-written analysis, "The Facebook Fallacy." It's really the inevitable question: what happens when the price of advertising goes to zero? How is that a viable business model? 

Facebook's "disappointing" IPO -- like so many IPOs that failed to live up to expectations, Vonage comes to mind here -- is a key indicator of bubbles ready to burst. Like Abe Lincoln said, you can't fool all the people all the time. But over the past 20 years, the Internet has come pretty close.