I just noticed that Yahoo is allowing users to block search results. You click the “block” link and this prevents the result from showing up in future searches.
I can see Yahoo using this data to implement Bayesian filtering for personalized web searches. As people continue to block and save sites in My Web, the filter gradually will define what people see as spam or relevant.
Although this data may be used to influence Yahoo’s general search rankings, I believe this will remain a personalization feature. Since Bayesian filtering is trained on a personal basis, there is no need to extend the training to the general index. Keeping the training on a per user basis, will minimize spam use of the block link.
Update: Rand is going to block About.com from his searches.