londrum - 5:55 pm on Feb 25, 2010 (gmt 0)
it might have something to do with it... if you're getting more click throughs from the search results now then you've basically given google a better opportunity to weight your site. if you've got a high bounce through rate, with people returning straight to google, then presumabely they are measuring that and counting it against you.
that wouldn't show up in the analysis you did, because your bounce through rate has always remained the same.
other sites like tedster's might not be affected in the same way, because they don't have such high bounce-through rates.