In addition to Tuna-Fish's excellent reply, bpodgursky, you need to ask yourself: what would be China's motive to destroy Bitcoin via a majority ("51%") attack?

In addition to Tuna-Fish's excellent reply, bpodgursky, you need to ask yourself: what would be China's motive to destroy Bitcoin via a majority ("51%") attack? They have no particular reason to do so. On the contrary, they can instead economically benefit from being a participant in the Bitcoin ASIC design and manufacturing industry. (And they already are: Avalon, Blackarrow, ASICMINER/BlockErupter, etc, all these companies are operating primarily out of China). Also: China "locking up" coins would do nothing to stop or destroy it. It would just drive the value of the remaining coins higher and as we are seeing right now, an appreciation drive the interest in Bitcoin up, not down.