I'm an advocate of mean answers, if they're well-placed. I've seen them work at kuro5hin.org; they're 'area effect' weapons against stupid posts (by example), stronger than just a downvote. The truth is, as a site grows, you really only want a subset of the readership posting, and you want the rest to think twice before doing it (that sounds bad, but if you want read-quality and not write-quantity, you've got to do something to make people pay attention). Now kuro5hin.org is pretty much dead, but I don't think that was the cause.
The trick is that we don't actually want to shame and anger people posting comments that don't fit into the HN ethos; we just want them to improve their comments, or wander off elsewhere without feeling too bad about it.
If someone has good ideas but is used to discussions on wilder forums, we want to educate them in a respectful way. If someone really doesn't belong here, we don't want to get their attention; we want to make HN as boring as possible to them, so they go away instead of posting a self-righteous rebuttal or seek vengeance in some way.
On the subject of respectful education... it might be helpful to have some built-in explanatory text shown next to downvoted posts shown only to the author, with the standard reasons for HN downvoting, and suitable responses for downvotes that seem unjustified.
