To be honest with you, getting a zero or a .5 is really easy, just send it some crap traffic and you will get it really easy. The problem is when you send them good traffic that's when I sometimes think they use the dartboard method.
It's more of a joke. Yahoo/Bing knows what crap traffic is, and they do a good job of that. It's what knowing is really good traffic versus average traffic that they have problems with.