During an Advertising Week panel on Monday, a moderator asked Facebook COO Sheryl Sandberg how the Wall Street meltdown will effect online spending. Sandberg delivered a carefully crafted response to an expected question touching upon her time at the Treasury during the Clinton years, the Mexican peso, the Asian crises of the 1990s, and contagion, a fancy new term the rest of us can break out at dinner parties. When she's so comfortable talking global economics, why did Sandberg ever leave Washington D.C.? Look how smoothly she endorses Treasury Secretary Hank Paulson. Most obvious of all: She's clearly enjoying herself. We don't get the same vibe from Sandberg when she's talking up Facebook.