There are a few places that take credit cards (I never used mine), and while there are a lot of automated teller machines, I only saw one place that accepted non-Chinese cards (the Beijing airport). The lack of usable ATM machines caused me an indirect problem - after a month in China, I forgot my ATM number! After a few days of hoping I'd remember it once I wasn't as sleepy, I gave up and got a new number. Naturally, when I walked up to an ATM two weeks later, I remembered the old number.
The point is that your credit cards, etc., aren't accepted very many places, so you should bring lots of money to China. But don't bring cash: bring traveler's checks - the banks give a better exchange rate for traveler's checks than they do for cash (counterfeiting is a big problem in China).
There aren't many places that accept traveler's checks, and you'll probably need to go to the main branch of the Bank of China to cash your traveler's checks. A side benefit of having traveler's checks is that the illegal money traders will stop bothering you once they realize you don't have foreign money. And don't bring cash to exchange with the illegal money traders: supposedly their rate isn't any better than the Bank of China (I don't know for sure since we didn't talk with them except to tell them we had traveler's checks), and my guess is that it's likely they'll give you counterfeit money. And it's illegal.
I recommend bringing a money belt to carry your cash. You probably want something else to carry smaller amounts that you expect to spend, but there are areas that are known for having pick-pockets, and a money belt is safer than other things. The money belt will be more uncomfortable than you'd think, though - the heat and humidity will cause you to sweat more, especially where the money belt presses against you. I.e., don't keep anything in the money belt that a bit of moisture would ruin.