From the about page:
“With an increasing number of people reading, writing, and commenting on blogs, finding relevant content has become increasingly difficult. For a variety of complex technical reasons, current blog search services deliver less-than-satisfying results. These reasons include an exclusive emphasis on freshness, or a too simplistic computation of a blogger’s authority. Our algorithm sorts through all those blogs, super fast, and finds relevant content to match a blog search query.”
TailRank is treading similar grounds, you need a log-in to participate, although you are able to surf around without one (my password doesn’t seem to get me in)…anyway more on this service later, it seems a little complex at first glance.