1. I don't think it has much to do with quantity of writing but quality of writing. Although posts that contain many paragraphs may seem like really strong posts, a post that has time taken out to think about the topic and how to word yourself seems like a far better post to me. Things seem to not only mean more but express more when they arent something that was written off the top of someones head. A good post is something that reveals the writers message, something that just clicks insides you and has you automatically thinking I get what they're trying to say whether you agree with it or not because that doesn't really matter, but what does matter is that you understand the message the writer is trying to convey and get through to the reader.
2. Ive posted about lots of things such as what book I'm reading or something a fellow classmate wrote, or even my everyday life in terms of commuting.