Is anyone checking their Webmaster Tools "Top Queries" data - especially the section that only becomes visible after clicking on the "+" next to the query term? I'm seeing a lot of variation in search position being reported. Even keywords that rank #1 a good bit of the time are also showing impressions from 8 or 10 other positions, including page 2 or 3.
If Google is now mixing things up a lot more (as it seems) that could account for a lot of what we're seeing. It seems to me that CTR from the organic SERPs has become quite important - and now we can see the data.