Google Search's preferences page includes the option to disable SearchWiki. Just click on the checkbox next to SearchWiki and you'll "hide the ability to share, promote, remove, comment, or add your own results".
If you like a less cluttered interface for Google's search results or you don't use SearchWiki, disable the option from the preferences page.
"SearchWiki lets you customize your Google Web Search results by ranking, removing, and adding notes to them. You'll see your changes whenever you do the same searches while signed in to your Google Account, or until you decide to undo them. You can also see how other users have tailored any given search results page with their own notes and changes," explains Google. The feature lets you personalize the search results and it's especially useful for repeated searches. Marissa Mayer says that "40% of searches on any given day are repeat searches for that user".