Patterns of recovery: Economist Roubini on the shapes of things to come

After predicting our current global financial crisis, New York University professor of economics Nouriel Roubini earned himself the nickname Dr. Doom. Roubini's words have the power to move markets; when he talks, people listen.

And lately, Roubini seems to have changed his tune somewhat, albeit with many caveats. He anticipates a possible "U-shaped" recovery, with leading economies undeperforming for as many as three years, but also warns of the increased risk of a "double-dip" scenario. "U-shaped," "L-shaped," "double-dip," "V-shaped" -- what do these terms mean?