Looks like another algo change is making it's ugly way through the serps. I don't think they'll ever settle out, in fact, I think Google wants to juggle them constantly which will result in sporadic traffic for all. This keeps their Adwords Ads in cycle. I foresee a day, very soon when serps are refreshed and changed as fast as a movie image - 30fps.
Every 30th of a second the serps will change and depending upon when you click, that's what you get.
As far as Adwords Ads, instead of position for 10 ads, the cycle would allow for 300 ads all served in split second, ever changing intervals. It would be very difficult to game that system.