Google is likely updating their search results, sites sometimes go up and down for no apparently reason. But i guess the blogs that now go down a bit are all rss feeded blogs, that likely see the effect of a content filter, you can read all about it on:
http://www.netpond.com/showthread.php?t=117099 . But that is just a guess, maybe it is just bad luck for a few of you.
At previous updates sites went up and down while the update was ongoing, so i would suggest wait a few weeks until the update is completed.