I've been wondering this lately too. I've heard everywhere that you should put as many tags as possible in your tags area, but now I'm not so sure. I'm almost thinking it basically splits tag weight between all your tags, so the more you put in the tags area the less heavily weighted each are, which actually hurts your searchability.
It would be nice if they would shed light on this if they did indeed change it since it's the opposite of what they say in the handbook.