The dot com bubble of the 1990s was marked by a "growth-over-profits" mentality. During that period,  Web entrepreneurs made "free-money" selling popular, but hugely over-valued dot coms in initial public offerings to people who either didn't understand or didn't care that these businesses were never going to turn an actual profit. Today, websites like Facebook, Twitter and Pandora are each valued in the billions (and tens of billions), and are expected to go public soon. Is history repeating itself; and if so, should we be worried about a second (or is it third?) dot com bubble? For the answer we speak to   Louise Story, finance reporter for The New York Times, and Duff McDonald, contributing editor to Fortune Magazine.