Comments are categories

Tags are categories.

I think xamdam meant that there should be a category of "lighter" posts that people could opt out of (ie, not see in their feed of new posts) so that they wouldn't have the right to complain that they didn't live up to their expectations. Promotion means that there are two tiers, but I'm not sure whether people read the front page or the new posts.

Incidentally, I think people are using the tags too much for subject matter and not enough for indicating this kind of weight or type of post. For example, I don't see a tag for self-experimentation. If the tags were visible in the article editing mode, that would encourage people to reuse the same tags, which is important for making them function (thought maybe retagging is the only way to go). If predefined tags were visible in the article editing mode, that would encourage posts on those topics; in particular, it could be used to indicate that some things are acceptable, as in Anna's list above.