they make the same mistake here that everybody else makes with tagging. if you look at the research on tagging, the big tagging success story was delicious - which leveraged SELF-INTEREST in its tagging system and produced a useful public resource as an emergent byproduct. this is not coincidence! read James Surowiecki. seriously. economics 101 for social software.
leveraging independent self-interest is THE key factor which differentiates the wisdom of crowds from the stupidity of groupthink. "the wisdom of crowds" is really just a reiteration of adam smith's invisible hand. to create an invisible hand effect, you must leverage independent self-interest within a shared context where independent self-interested actions are visible to other independent self-interested agents.
every tagging system that fails to leverage self-interest fails to capture that. you can't just sprinkle magic web 2.0 fairy dust on something and go "Tagging!" if you want delicious results, you have to find out what made delicious work and emulate that. what made delicious work was a fundamental principle of economics. the reason so many sites have useless tags is that their makers are ignoring this fundamental principle. it's cargo cult site design.
similarly, this flagging nonsense flat-out ignores another basic fundamental of economics. what makes it even more insane is that Paul Graham already explained in one of his first blog posts about Bayesian filtering exactly why spam filters should be tuned to an individual's preferences and not to a group's. if you had a bunch of individually-tuned spam filters, you could find a way to leverage that. since you have a group-tuned spam filter, you have nothing but a tragedy of the commons magnet.
anyway, just ranting about why Hacker News should hurry up and cease to exist already.
edit: just for the record I'm responding to Reg's comment. I don't know if that's clear from the UI. it is a non sequitur rant, but it's not a complete non sequitur rant.