Strongly recommend using ATMs for money. The big charge will usually come from the U.S. bank, with the Chinese bank generally charging a 1% fee on top of that (unless you find a Chinese bank that has a no-fee arrangement with your U.S. bank, such as Bank of America and China Construction Bank).

When changing RMB to back foreign currency, the rule seems to be that you don't need receipts for amounts under US$500. As with most rules in China, though, the actual application depends on the user... also, you should be able to change RMB to foreign currency at major banks outside of China, at least in modest amounts (I have changed RMB to Hong Kong Dollars at HKG and I have changed RMB to Euros at the Bank of Ireland).