I have great admiration for the US constitutional system, and I think that there is a lot that China can learn from it.
One thing that I admire about the constitutional system is how it is reacted to the Bush administration's efforts to override "due process". It is the unfortunate situation, that the Bush administration has been able to detain people at Guantanamo without trial, but at the same time it is refreshing and comforting to see how the system has fought back against extensive claims of executive authority. The restrictions on civil liberties that have resulted from 9/11 are unfortunate, but if you look at some of what was proposed immediately after 9/11, they could have been a lot, lot worse. The case against Jose Padilla was obviously a test case, and had things gone differently in that case, the results would have been very frightening. Fortunately, the system reacted against it, and it seems pretty obvious that future cases involving US citizens on US soil will likely go through the Federal court system. Part of the reason this matters to me is that I can imagine some scenarios where without the "due process" protections of the court system, I'd end up behind bars (suppose you end up with anti-terrorist military tribunals + bad relations with the PRC + the non-sense that Wen Ho Lee went through -> I'm in trouble).
What I do find interesting (and important for Chinese constitutional development) is where the resistance has come from. By and large, it hasn't come from some mass popular uprising, and it's only been in the last few months that the political opposition has made this much of an issue. Where the main resistance against military tribunals and detention without trial has come from is within the system, from military and civilian attorneys and judges just doing their jobs. The implication that this has for my thinking is that it suggests that if you want to avoid abuse of power, the important thing is not to try to instigate a mass uprising, but rather to strengthen the institutional framework of the judicial system.