Google: Current Algo Update-Dance -> High Rankings Search Engine Optimization Forum: "believe that it is not a simple matter of the hilltop algorithm,.. there is much more in play here. Another interesting algorithm is the Topic-Sensitive-Pagerank algorithm. This algorithm consideres up to 16 or more different PageRank factors.
The original PageRank formula considered only 1 factor. It also failed to recognize any unrelated links. Google tried to compensate for this with things like looking at the anchor text,.. but all these things were just minor updates to compensate for what the original PageRank was missing. This new update does a much better job as it improved determination of relevancy of a back link"