Mixed blessings for SEM come from a Boston University study entitled Traffic Characteristics and Communication Patterns in the Blogosphere.
First, the good news: the majority of blog traffic comes from search engines. Search engines accounted for 43% of referral traffic in the blogosphere. Hurray for search engine marketers! Their diagram of referral traffic (below) does not include the 28% of blogosphere traffic without any referral data (probably bookmark or type-in traffic).
Now for the bad news: “Despite the intimacy between traffic and search, however, optimizing a blog for search engine algorithms does not win the blogs retention or popularity,” as MarketingVOX put it. Yep, all the rankings in the world don’t make your blog well read, popular or sticky. You have to do that.