China is up over +20% while US is down -20% ytd. That is because they are stimulating the economy while the US is propping up undead zombie banks. According to Bloomberg, China is spending billions or trillions on building new infrastructure, boosting manufacturing, reducing taxes on stock trades, reducing taxes on consumption and exports. Meanwhile the US is doing the opposite. Instead of stimulating the economy, they've used billions or trillions on FNM, C, BAC, AIG, etc... and two wars in the middle east. They're also considering raising taxes on stock transactions. That is why China is up 20 and the US is down 20.
China is announcing all sorts of additional stimuli, including cutting stamp duty on stock trades, additional consumption expenditure, etc. What would be interesting is if they start using the current juncture as an opportunity to buy commodities (they've already started doing that). Oil going to $100 now would probably be the final nail in the West's coffin.
You deal with China's number the same way you deal with US's number. Look at individual companies, their reports as an aggregate tell you everything you need to know.
Copper demand is slowing significantly in China. Now, the Chinese Government has to decide whether to unfurl another stimulus package, which was far more effective at $550 billion, because it directly targeted consumers, than our boondoggle was.