The whole PageRank conundrum reminds me of the parable in Gödel Escher Bach about the phonograph that breaks when you play a specific well designed record. GEB was referring to incompleteness but it's an equally good metaphor for computer security and quality-algorithms like PageRank. If there's sufficient motivation to find your algorithm's weak points and exploit them, it's going to happen. Complicated algorithms just require more complicated and better designed inputs.