In general, the expectations seem to be loose, which makes sense. However, are some things I've noticed from looking around and commenting:
1) If your comment is just a joke or an agreement, people won't like it. There's a guideline for group comedy that you shouldn't just agree, you should "Yes, and..." meaning to agree and contribute. While agreement isn't (always) mandatory, agree and enhance seem to be the norm.
2) Sources. Sources, sources and more sources. People love sources! Even when they don't read them!
3) Honestly, when talking to mk about features, keep in mind that he made all of this possible. And maybe thenewgreen. I'm not sure about that one, that's just context clues. It sounds like I'm saying they're fragile, but really I'm saying they deserve all of the respect you can muster. Unless you're syncretic or kleinbl00 or Saydrah or something, because all those guys seem to have a billion ideas for the site and some kinda understanding among each other. Maybe this isn't a rule, but still, I think respect in general should be on this list and if you can't do it for everyone, do it for mk.
4) Not everyone is as open-minded as we all pretend. Sometimes you'll run into someone where both you and they are not going to yield on the issue at hand. At that point, it's probably better to walk away, ignore, and move on.
5) To get a great feel about what's promoted and what's looked down on, try checking the "badges" link under the "discover" section. Or look at "recently badged/ most badged" to find users who have been/are routinely rewarded for outstanding badges. (This sounds super braggy, since I am the most recently badged person, but it really can give you a feel for the sight.)
6) We don't seem to have a list of "don'ts" but on that list we don't have is definitely beating women. I'm glad about that, and I think the overwhelming majority of the users I've seen/interact with would be deeply unhappy to see anything headed in that direction.
1) Watch out for religion.
2) Sometimes people are jerks!
3) Some people are the smartest people they've ever met. Be careful! You might be one of these as well! I might be one of these as well (in that I act like a jerk sometimes).
Having said that stuff, I think that kleinbl00 has made this point before, but fuck what other people want. Post what you find interesting/important. Speak your mind to anyone who speaks otherwise, however you feel is appropriate. That's the only way to find out if this is the community for you. If you're not enjoying it, leave! It's a website, not a job.