Honestly, I am not sure that this is even possible. First of all, we cannot talk about "quality" as something common and understood for everybody the same way. Every person would put his own meaning in this term. For some users a good and appropriate joke would be considered as quality post, for others such a title would apply only to sharing some new, authentic and widespread useful information. That is a very serious issue, as for me. Because many forum member, especially those who try to improve quality of posting here not just for themselves, but also for other members as well, usually give explanation, what they mean by quality. For example, 1miau did so, and I think it is the right thing to do, because without this criteria it would be impossible to really understand what someone is thinking about while talking about improving posting quality.

The second thing I would like to pay your attention to is that not all of user`s post will be the same quality. We are all people, and a lot of things affect the way we think and write. But the general posting history could be more or less qualified, I agree with that. And the main task for us as forum members is to make the whole picture of our positing quality, useful and interesting for ourselves and the others. But concentration on every single post wouldn't help a lot, in my opinion, because it would feel like a lot of pressure and could kill the motivation to continue writing.