According to the latest Pew poll on US attitudes on international affairs, 44% of Americans think that the world's leading economic power is... China. Only 27% think it's the United States. Here's the somewhat blurry chart from the report.

As Barack Obama would say: Let me be clear. People who think this are crazy. Or, to be more gentle, they are really woefully misinformed about what the world is like.
You could address this point with, you know, "facts." Almost no one in the United States is a peasant farmer. Most people in China are. Nearly everyone in America has indoor plumbing. Most people in China don't. Japan has one-tenth as many people as China, yet its economy is larger -- the second largest in the world. America's is of course largest of all, three times larger than Japan's and about four times larger than China's. Name 20 large American corporations that do business worldwide. Without trying, you can probably name 50. Try to name even 10 from China. Name the most recent winner of a Nobel prize in science from a Chinese university or research institution. (Hint: this is a trick question.)
But visual aids may somehow convey messages that "facts" don't get across. Toward that end, it's worth checking out a much-circulated recent post on the ChinaSmack blog -- a site that translates popular Chinese posts into English. It's about practical living circumstances in a Beijing elite university district.** Here's a sample photo:
It ain't Princeton.