You have to have a minimum karma score to be able to downvote. I'm not sure what that score is though.

Thanks. To be honest, one of the things i liked most about HN was the lack of downvoting (I never realised it was possible...i thought the grey posts were caused by mods or something). I know in effect there's no real difference...but the whole place felt more 'community' like. Ah well.

The min threshhold I think is now 500 karma. It's a way to ensure that only people who have been around for a while and understand the community have the ability to downvote, and the rule is only downvote contentless posts (like memes, "+1"'s, etc).

Jasus, i'll never get to 500. Those rules make sense, but the parent comment in this thread had been downvoted despite being correct. Fairly Redditish (the one thing that puts me off Reddit). Thanks anyway.

It's pretty easy to accidentally click the downvote button, and there is no way to fix it. Usually someone will vote it back up in short order.

Rudeness gets downvoted pretty aggressively.