Actually, I thought it was Albania -- which was for a while the only "officially" atheist country in the world, but checking up on Wikipedia, once Islam was made legal again, it seems to be back to developing-nation levels of religious activity.

So, yes, you're right, it's China. At a rough pulling-numbers-out-of-a-hat, China will be back in sync with the rest of the world average (for levels of religious activity) somewhere around 2050, when it will be mostly Christian and Buddhist.