Just to explain... The way the pattern is the same on not just a couple of sites, but all the top sites, no matter what type of site it is (news, aggregator, forum, blog) should make any webmaster jump. Sometimes you will see trends on similar type of sites, like bloggers on a certain platform dropping for a month or forums dropping, but all of these types of sites at the same time really is a head scratcher- especially when looking at left leaning website's rankings for the same period.