Not sure how helpful this is, but yesterday was the first time I've seen a marked drop in traffic for one of my sites. Not an ecommerce site, went from about 100/day to 1 yesterday.
SERP results today look a little lower than usual for long tails, but my main 3-word keys are good.
The site is informational, built using WP with very little modifications, but two days ago I did update it to new version and switched the them to default 2011 theme as a test.
I've now switched back, waiting to see what happens.