As of late yesterday afternoon I noticed a few minor hiccups in the Google SERPs. This morning those hiccups escalated into multi-page jumps, old versions of pages re-entering the index, pages being dropped from the index and different results appearing with a click of the refresh button. It is far too early to even try to predict what type of update is underway or what it means but hang on to your hats as it looks like a fairly bumpy ride.
And note – if you see your site drop or jump up in the results – don’t count on that staying as we’re seeing bouncing in both directions and my prediction (the only one I’ll make at this early stage) is that what we’re seeing in both instances is not what we’ll see at the end of the day.
Good luck !