Sgt_Kickaxe - 6:26 am on May 30, 2010 (gmt 0)
301 redirects, too many of them to the same location such as with a sitewide "special offer" to an affiliate program. Affiliate spam is increasing, everywhere including social networks, cut down on the volume you offer and increase the ratio of "no affiliate offers on this one" pages.
Speculation of course but so says my stats. Pages dropped in rank all had the same link to a redirect file, the pages that didn't are still rocking. Mayday is anti affiliate imo. If there's one thing Google loves above all else it's purity.