The thing to remember with the yuan peg is that the Chinese have maintained it, whether the USD is strong or weak. They have been consistent. When the USD is weak, all the other countries cry foul, but when the USD is strong (i.e. during the credit crunch), they all go quiet.
There's something awfully symbiotic, or parasitic, about the US/China relationship. The drug dealer has a client who can't stop buying, but can't afford to pay.. so the dealer accepts IOUs from the user in return for further narcotics.
The profit margins in Chinese industries are tighter than people imagine, so (for example) a 10% increase in the value of the yuan will hurt many Chinese exporters. However, the inescapable truth is that people in the US (and UK) get paid far more than people in China do, for producing exactly the same output, whether it's pyhsical goods or even a service (computer programmers, e.g.). This is the issue that has to be resolved over the next decade or two.