China's economic growth topped 11 percent in the first quarter, which is pretty darn fast. For comparison, we think that long-run U.S. growth is about 3 percent. (Both figures are inflation adjusted.)
There are skeptics. Macroblog has a good commentary on some of the limitations involved.
I'm preparing an in-depth commentary for a future issue of the Businomics Audio Magazine. The gist of my current thinking is that China's growth will continue for some time, but long before they surpass the U.S. or European economies, they'll be constrained by a wide variety of institutional limitations.