I see the credits thing is happening but had a thought about displaying a score of post quality. This could just involve the number of posts divided by word count or character count or some other text scoring system (like in MS Word). Could also incorporate the votes on a post by readers. This would very quickly show up anyone using short "thankyou" posts to get their count up.

Or this could be the purpose of the Credit system (although you can buy credits - you cant buy a quality post score) which would make this useless.

Just my 2 cents...