I've seen some serious dancing over the last several days. Sites I have that haven't shown up on the top 10 for literally years are now showing in the results. A site I had which was being de-duplicated by Google, and finally showd up on its own, just got re-duplicated (i.e., doesn't show in the serps unless you put, &filter=0 on the search query). The page hasn't changed. It was spidered on the 18th, updated on the 19th, not spidered again until 23 Sept, but still shows 18 Sept cache. Spidered again on 26 Sept, again on 27 Sept. Google finally caches the 27 sept copy on the 8th, but then reverts to the 18 Sept cache on the 30th. It's odd, and I don't particularly have an explanation except cache.
I've heard the same thing from some of my co-webmasters. Somebody even reported a new PR to their website, which I have yet to confirm.