So, Matt Cutts confirmed it was a glitch on webmasterworld, with raw data escaping into the index before it had all the correct quality signals applied.
I don’t consider those rankings indicative of anything coming in the future. Some data went into the index without all of our quality signals incorporated, and it should be mostly back to normal and continuing to get back to normal over the course of the day.
Lots of people will be very happy to hear that.
We still have some fairly radical changes in places on clients sites and are not wholly convinced they’re all going to return, we will see I suppose.
Edit new info. as always things aren’t quite so simple. 
Google search update blows up, results rolling back now
there is still talk of updates to come, although Google deny this.
