Angry Bear has some good posts and comments here and here on the RMB revaluation, and specifically the issue of the fixed exchange rate that China adhered to for ten years.
Here's my two cents on why the Chinese government stuck with a fixed exchange rate for so long (and why major exhange rate changes in the future will occur by government fiat at carefully chosen intervals, and not as the result of a "free float").
I think the Chinese government clung to the 8.28:1 exchange rate for so many years because it wanted to discourage speculation while encouraging a relatively unfettered export trade.
Their forex regime is designed to make things reasonably uncomplicated on the current account, with the understanding that with a fixed exchange rate it's not worthwhile for importers and exporters to game the system with fake import and export contracts that would allow them to cycle dollars through their businesses and take advantage of the pre/post revaluation spreads.
The ingenuity of China-based enterprises in coming up with scams like this is limitless. The art is already highly developed in the techniques of transfer pricing to sequester funds overseas to reduce stated profits and to enable the offshore purchase and reinvoicing of imports at artificially low prices before they crossed the Chinese customs gate.
A fixed exchange rate was preferable to the enforcement headaches and bruising of the precious entrepreneurial spirit that would be required in trying to crack down on the fraud (abetted by corrupt government tipsters) and flood of illegal speculative cash that would accompany a fluctuating exchange rate.
As the Chinese government always takes pains to point out, it didn't manipulate the RMB/US$ exchange rate, as the U.S. has accused it of doing. It did just the opposite and had kept the rate fixed where it was since 1995 even as the value of the dollar drifted away.
That the Chinese government had to bow to political pressure and discard this stable system for one in which the currency becomes more vulnerable to speculative attack is a fact that probably doesn't make them very happy.
I wonder if the People's Bank of China will surrender to the guilty pleasure of confounding current and potential speculators with a transitory devaluation--a bull trap, you might say-- but I don't think the momentary satisfaction would be worth the international dismay that such an overt manipulation of the forex regime would evoke.