Look what I found casascius suggested some time ago (2011), and, wonder what, he was thinking of a hypothetical MtGox 500K BTC screw-up. Boy, did he misunderestimate MtGox 
Imagine this were 500000 BTC and every MtGox user were at risk of a major loss. (which would certainly hit the news and damage the community).
A feature that allowed a miner to vote out a block or a transaction would be valuable. If 50%+ did it, the error would simply vanish. Democracy at work. But it would only work if that 50% voted immediately.
A feature that allowed a miner to vote out a block or a transaction would be valuable. If 50%+ did it, the error would simply vanish. Democracy at work. But it would only work if that 50% voted immediately.