First, some members noticed a PageRank change, but we noticed that last week.
Other people are seeing some sitelink anomalies:
I have noticed that the numbers of indexed URLs from the sitemaps of my main site have been steadily reduced in the last two days. The reduction rate is about 5% per day. This drop takes place in all sub-directories and also shows on the results of a site command search. However, it seems that the fully indexed pages are not affected.
Additional observations include a change in the link: results and a few substantial drops in rankings (in one case, from #2 to #39).
Forum discussion continues at WebmasterWorld.