The social bookmarking tip from different IP addresses is particularly useful. My question is the differentiating between those pages which pass PageRank, those that Google would deam as "authorities" (anyone can post a link on Facebook, but only certain people get a Yahoo Directory link for example) and those which are a waste of time!
You obviously put a lot of work into that post and its very interesting to see the thought process that you went through to come up with those conclusion. Thanks for sharing your deep thoughts. I must admit that I think you nailed it on this one.