Positive feedback is great in reinforcing good behavior, for sure. I think the difference is when positive feedback about a coworker is directed towards management which, since there's an adversarial nature underlying most workplaces, you are acting as someone else's public relations spokesperson for free. I'm not saying that people should never point out the excellence of their coworkers to management; what I'm saying is that the mechanics of the workplace make this behavior rare and simply not worth the effort in most cases. The safest thought pattern for one's sanity is to give praise, but never expect that praise to be reciprocated.