SearchWiki is a tool that allows you to collect your own opinions about web pages on a searched topic and to share notes with others. A logged-in Google user can push up an item in their Google search results to the top of the page or eliminate it from the results altogether. Google users can also leave comments on a given link or add a link of their own by typing it into a box at the bottom of the search page. The primary use of this feature is to serve as a note-taker for an individual person, similar to a social bookmarking tool which can be set to private mode if you wish.
SearchWiki will be more interesting as more people use it and comment on searches. As Google collects SearchWiki content, it's building a kind of stealth social bookmarking service on a much more useful scale.
I have dabbled with it but not used it that much, mainly because I forget about it, but I think it could become a useful tool. SearchWiki Help