I have been seeing some chatter at WebmasterWorld and other sources of a possible update that is being pushed out slowly since late October 31st through today.
If you read the thread, you'll see some people complaining about declines in rankings between the dates of November 1st and today. You will also see people excited about increases in rankings.
All the Google tracking tools don't show heavy fluctuations, with the exception of SERPs.com, which seems to have some bug. But the most, they show some activity on October 31st and November 1st, quiet down on the 2nd and 3rd. A spike back up on November 4th and today with chatter.
Here are some quotes from webmasters noticing fluctuations in the Google search results:
Been smashed by whatever rolled out. a good 20-25%
Yes, something is going on. One site's traffic slightly down and slightly up for another.
Quite a large drop in traffic overnight, not sure whether halloween would have this sort of impact. anyone else picking up anything? saw a large KB per day increase on Monday.
Truth is, I am not sure I'd classify this as a significant update but let's see if Google announces anything.
Forum discussion at WebmasterWorld.