If black hat seos started to believe Google was paying specific attention to Delicious bookmarks, Delicious would be flooded with fake accounts faster than you can say "link farm".
History of search:
1. New company releases new search engine, better than the competition because it pays attention to a previously ignored signal.
2. Seos work out how to game the signal.
3. New search engine is now as crappy as the search engines it replaced.
Really, internet search is like macroeconomics: soon after you understand {how to prevent recessions, how to find the best webpages}, the problem vanishes and is replaced by something even more complex and incomprehensible. Furthermore, this has already happened.
This has interesting implications, I think, in the business of search.
It's almost like a negative network effect. The more people that use a search engine, the more people try to game it, and the less useful it becomes for finding what you want. This seems like it'd make things much easier for new competitors like duck-duck-go to bring a superior product... at least until they gained enough market share to be worth SEO time gaming.
You're quite right. But pretty much every strategy a search engine uses is susceptible to black hat SEO. I think there's something to be said about having the system use how others are reacting to your comments rather than just what your content is and who links to it. Yes, you could farm out Delicious accounts and have them bookmark your site, but from a SE perspective it's easier to remedy this problem (Delicious requiring captchas periodically, looking for accounts which have an uncanny amount of similar bookmarks in a span of time, etc) than it is to come up with strange rules about content that the black hat is free to change.
Judging by the votes, apparently it is more valuable to point out why a certain idea might not work, even if all of the alternatives have the same problem, than it is to suggest something with exciting possibilities. Nothing against you, personally -- your comment is quite right and I agree gaming is a major concern.
History of search:
1. New company releases new search engine, better than the competition because it pays attention to a previously ignored signal.
2. Seos work out how to game the signal.
3. New search engine is now as crappy as the search engines it replaced.
Really, internet search is like macroeconomics: soon after you understand {how to prevent recessions, how to find the best webpages}, the problem vanishes and is replaced by something even more complex and incomprehensible. Furthermore, this has already happened.