You can give positive rep or neg rep. Everyone starts off with 10 rep points , if you get 100 rep points + 500 posts you get a different coloured name like I don't know like , green ? Yay or nay idea ?
Nay. Because... I can't really see it ending up well. Because it would, in the end, risk leading to cliquishness: "I'll give you rep and you'll give me! also, we don't like those guys over there, so we'll join forces to give them negative rep!". Even worse, we try to have a very low threshold: You can come in with whatever question you have, feel free to contribute with whatever advice you want to give! If people start worrying "oh dear, if I ask a stupid question I'll lose rep and everyone will think I'm useless" or "I'm afraid to give advice because if it's bad I'll be smacked down!", then we risk losing that. So... I'm OK with a social network site having this, and while I like this site as a social environment, it's not really what we're about.
The idea has come up many times, and the general consensus of the staff is that what makes EC great is that everyone who gives advice here does so because of the intrinsic satisfaction they get out of giving advice. Adding a rep system would add extrinsic motivators for giving advice, and people would start giving advice for reasons other than because they feel they have something useful/helpful/supportive to say. In other words, it would reduce the quality of the support being given here, and being that we're a support community, that's not exactly in our best interests.