Look at mwaser: he complains a lot about being downvoted, but he also got a lot of feedback for what people found lacking in his post. Yes, a portion of the downvotes he gets may be due to factors unrelated to the quality of his arguments (he repeatedly promotes his own blog, and complains about the downvotes being a proof of community irrationality - both can get under people's skin), which is a bit unfortunate, but not a fatal flaw of the karma system.
I did. The feedback that actually told him something came as replies. I'm not seeing how the use of downvotes actually helped there, and it did seem to add unnecessary nastiness to the exchange.
I agree it's a bit harsh, and not always useful. It's a bit of a pity that the karma system doesn't allow to make a difference between "5 people found this post not-that-great" and "5 people found this post absolutely terrible".
Maybe it would be nice to have a system that would allow for more nuance, but it would also have to be easy enough to understand and use, and not be easy to game.
Also, I would say that the downvotes did have some utility, by expressing "you should pay more attention to criticism, most people here disagree with you".
[Update: and now there's a fifth discussion thread, which you should probably use in preference to this one. Later update: and a sixth -- in the discussion section, which is where these threads are living for now on. Also: tag for HP threads in the main section, and tag for HP threads in the discussion section.]
The third discussion thread is above 500 comments now, just like the others, so it's time for a new one. Predecessors: one, two, three. For anyone who's been on Mars and doesn't know what this is about: it's Eliezer's remarkable Harry Potter fanfic.
Spoiler warning and helpful suggestion (copied from those in the earlier threads):
Spoiler Warning: this thread contains unrot13'd spoilers for Harry Potter and the Methods of Rationality up to the current chapter and for the original Harry Potter series. Please continue to use rot13 for spoilers to other works of fiction, or if you have insider knowledge of future chapters of Harry Potter and the Methods of Rationality.
A suggestion: mention at the top of your comment which chapter you're commenting on, or what chapter you're up to, so that people can understand the context of your comment even after more chapters have been posted. This can also help people avoid reading spoilers for a new chapter before they realize that there is a new chapter.