Have you seen Promote, Remove and Comment buttons near the Google search results, when you have logged in with Google. What are these buttons? It’s a Google feature called SearchWiki, a way for you to customize search by re-ranking, deleting, adding, and commenting on search results.
Basically this is not available for all searchers, to use this feature you have to signed-in Google account (Gmail, igoogle or anything). With this feature you can move the results to the top (using Promote arrow) or remove a site using the delete (‘X’ button) that you don’t feel belong. You can also write notes attached to a particular site. Changes you make to the search results are stored in your Google Account, these modifications will be shown to you every time you do same search.
Important thing to note with SearchWiki is that the changes you make only affect your own searches, not others.