After installing the plugin you are ready to block spam. When ever you’ll perform a web search, there will be an option to “Block site-domain” As shown in above figure. Simply click the option and all the results will be hidden from that domain. You may also restrict to sub-domain also.
If you wish to see the results you may have option to edit the subdomains or Unblock completely, as shown in above image.
If you have blocked a lot of sites and want to see the original result you can click “Show” link at the footer of search result.
According to Amit Agarwal the results has not blocked on the server but hidden on your PC using some smart CSS, as tweeted on Feb 15th. Although this extension is not heavier in codes and functionality but it may be very useful tool to stay away from some spam-sites.
Beside this plugin their is another plugin that allows you to flag as spam and report Google, you may install is “Google Webspam Report (by Google)” to do so.