Anyone that claims the Chinese would walk over the US doesn't know a whole lot about the Chinese's recent military history. Sure they have one of the fastest growing economies in the world, but you know why? Because they have been living in the stone age up until the past 20 years or so. An economy can only grow fast that has lied dormant most of its modern life. There is nowhere else for it go. There economy and infastructure is still light years behind the US and other developed countries so using that as an excuse is ridiculous. China still has many years to go before it is on the same stage as Western Nations and Japan. The only advantage they have is their size, both geographically and population wise. All of their technology, wealth, and success can be attributed to the investment and knowledge of Western countries.
There large army wouldn't do any good unless the US invaded China, and I think we all know that isn't ever going to happen. Even if it did, the Japanese sure never had a problem walking all over them. People believe this hype and mystery that China is some superpower unstoppable beast that is just waiting to attack, when in reality, they are simply a growing country that has some old Soviet weapons and nuclear capabilities. They have the capability of being a superpower, but they aren't there yet. Plus, if they did attack, that could easily start a world war, with all of the hostility in nearby countries (N. Korea, Japanese/Chinese history, etc.).