As to revaluing the Yuan. China likes thing s like they are at present unfortunately that is NOT sustainable (See Krugman's comments about what he expects to be a Rapid plunge of the US Dollar:
http://krugman.blogs.nytimes.com/2007/09/20/is-this-the-wile-e-coyote-moment/Thus the big issue for China is HOW FAST to let the Yuan increase in value compared to the US Dollar. A slow change would give China manufacturers an opportunity to adjust to the lower profits that will result as the Dollar declines in relations to the Yuan. If it is fast, China manufactures may find themselves simply cut off from the US market to their costs being to high i.e. one day, the Yuan -Dollar exchange rate is what it is at present, the next day the Yuan to Dollar is 10 times what it was the day before. The price stays the same in Dollar terms, but in Yuan terms that is 1/10 of what it had been. Can these manufactures compete at the new price? I doubt it, which will forces massive bankruptcies in China and a rough economic times for China's working class.
A further factor is, at present, Oil is priced in Dollars. China has plenty of Dollars, but if OPEC says we what paid in Euros, those Dollars become worthless to buy oil with. China may then just dump them on the world market and with that move kill any chance of Bush being able to continue the war in Iraq do to lack of funds (i.e. the US will NOT be able to sell any new bonds, for the OLD US bonds would set the price for the new bonds and that will be Zero or close to it).
Buck to the Yuan, if Krugman is Right and the US Dollar will undergo a rapid plunge in value, OPEC will drop the Dollar as a currency (making the fall of the Dollar even more drastic) replacing it with the Yen, The Euro or maybe even the Yuan (Through most OPEC trade is with Europe so the smart money is on the Euro). China is a NET importer of oil, and if the yuan stays tied in with the Dollar, the Yuan will fall with the Dollar, making Oil more expensive to China. Breaking the yuan from the Dollar will minimize this problem.
Thus what I foresee is a Rapid decline in the Dollar, followed by a OPEC dropping the Dollar and then China letting the Yuan float in relations to the Dollar. I do NOT know when this will start (Neither does Krugman) but once it starts it will feed on itself till it is finish. I.e. the Dollar drops, OPEC drops the Dollar, the Dollar drops again, China frees the Yuan from the Dollar, the Dollar drops again. The Dollar is bottom out, but where? no one knows.