There are two threads at WebmasterWorld forums talking about a Google shift. The first is named 17 Aug - restored pre-27 June positions and the second is named 17 Aug - Supplemental again.
It appears that everyone agrees that the Google results have shifted a bunch the night of August 16th. It also appears that although it may appear that the supplemental of old are back, they aren't. Senior WebmasterWorld member, g1smd, says;
I see many recently created new Supplemental Results representing content from just a few months ago. These are where the content has been edited very recently (and searches for the new content point to a non-Supplemntal Result), or where on-site duplicate content existed but the alternative (non Supplemental) URLs have now been filtered out (in one case the filtering was through robots directives to get certain URL formats delisted).
This confirms what we reported on last week that we should Expect "Fresher Supplemental Results" At Google.com.
Some people are happy with the results and some are not. Of course, the ones that are happy are less vocal than the ones that are unhappy.
Forum discussion at WebmasterWorld threads "17 Aug - restored pre-27 June positions" & "17 Aug - Supplemental again". Also forum discussion at DigitalPoint Forums.