OK, the long and the short of linking is this. To rank for a competitive term you need links. Links are like votes and votes win seats, or in this case search engine positions. Setting aside all the follow, no follow, pagerank blah blah blah, links are the life blood of the search engine algos. The problem is, the market for link building is so established that it's simply getting harder and harder for the algos to figure out what's a good link and what isn't.
Search for any competitive term and you will find sites in the top ten with links that tick every spam indicator box available. Respectable blogs warn of the dangers of buying links and link spamming, I'm warning of the dangers of doing it, the problem is, nobody told the sites dominating the serps that they shouldn't be doing it!
I know I bang on about link spam but if it's the dominant metric in the algos then the big G has to reassure us some more that the ethical approach will be rewarded because ethical SEO's clients want some answers!