I am seeing  one of our sites www.medicarebenefitsdirect.com got hit hard.  We just joined Yahoo directory and noticed a huge drop.  Also, noticed we are getting a ton of incoming links that we did not do.  We were ranked in top 30 even top 10 on many keywords in the medicare supplemental category.   Is there a major hole in this algorithm where you could possibly spam links to other sites triggering a SERP filter for targeted keywords.  We notice this change recently after getting listed in Yahoo directory.