My version of being Nice and Respectful tends to skew toward "if you don't have anything nice to say, don't say anything at all".
Which topics still have a good experience on Quora? I find the quality of the discussion, especially the quality of many of the questions themselves, to be quite low. They need more aggressive community moderation to filter out duplicates, miscategorizations and nonsense before potential answerers are notified/requested. It makes the site look bad.
Almost every day I get an email that says something like "nerflad, so-and-so requested your answer to the question 'how dows computer work?'". Nearly all of the music questions are especially asinine and I just don't have the patience.
Like so many others, I have completely stopped using Quora. Yes, occasionally there are still diamonds in the rough and Alan Kay will pop in to say something, but these kinds of interactions are the exception rather than the norm.
Stack Overflow's moderation is considered Draconian by a lot of people, but it's their lifeblood in my opinion. Q+A sites need a hedge against the descent into Yahoo Answers madness.