Wherever there is a reputation/ranking system on the forums, I can usually see 2 situations:
1. It's light and positive only (one cannot give a negative rating), so everyone gets more and more rep points. Everybody is happy, but this changes nothing.
2. With negative rankings added there are (of course not always) never ending threads/posts "why I have received bad rep for this/that?". People are complaining about the system abuse, unjust ratings given, etc. Even if a post/thread would be rated very low because it deserved it, there might be tensions between members, growing "aggression" and so on.

I think that at this point it would be safer for TalkFreelance to keep the "verbal" system of rating - ie. "thanks, good post/nice article" rather than introduce the real post/thread ranks.