So, here's how they do it. When you search you get different suggestions which changes over time and nowadays it is more often that ever before since they changed the way they can pull up SERPs. Thay are learning what people "want" from what they do after clicking on a result and from that they change/update/trim their stored results. It's as simple as that. It gets trickier when people don't use their suggestions since they have to learn how to incorporate that and show "good" results but they will eventually make a new suggestion out of it if enough people use the same query. You have probably seen how they can "twist" your query to try to "match" yours and steer you away to their stored results, "did you mean..." or even rewrite it, haven't you?
Peoples intent then becomes GOOG's intent and they will steer you towards what makes them money. GOOG are now stupid and they will do anything to "take over" any type of business that makes them money and use your work to do it. Zombie traffic? Nothing but GOOG testing things even though it looks like they come from "Far-Far-Away land" so if you have some type of money making site you can be sure GOOG will take it over somehow and use other info sites content to lure people in. I have said it before and got censured, but how long will it take before they go into the adult business (if they haven't already!)?
As for the SERP right now it seems like they have settled me at another level of traffic which is very low. In Statcounters Search Engine Wars they only have 25% and heve been for quite a while with a slight upswing the last couple of days. Last weekend the traffic went up and like a fool you think "Ahh GOOG loves me again..." but as usual it only last 1 day or two. I used to be really upset, but not anymore. You can't keep on chasing your tail to please GOOG because there is no way without money that you can please them.