Google has launched the functionality now for users to banish particular websites they have visited from ever appearing in their search results again. So while we have the Google +1 button endorsing sites we now have the option on the search engine results to reject and block sites.
For example searching the query "hotels in london" 208,000,000 results appear and select the result that has the search snippett that seems most relevant for the desired information or goal that you may want to complete. But when you enter the website you realise that this website is not the required information and would be of no relevance to you in the future so you return to the search results by clicking the back button. Now you can block that website from ever appearing on your search results again when signed into your Google account. A hyperlinked option will appear alongside the searh result "Block all www.domainname.com results" if you aren't signed into your Google account you will be prompted to do so, to block this site from any future search results that it may appear in. A site can be unblocked through the individuals Google Search Settings again if they wish.
This is yet another step on Google personalising results and also whilst they haven't stated is another way of weeding out poor quality sites, by letting visitors block sites that they did not find related to their search query. While this is a good automated way of letting Googlers provide feedback and dually personalising their results so they do not have to encounter the site again. If Google are using it as a ranking factor in their algorithm it is also a tool that is open for abuse.
It will be interesting to see in the coming months the impact this will have, as seemingly websites will not be provided with feedback as to how many times their website has been blocked by visitors. Further as of yet Google has not stated whether they are able to detect abuse of this tool by competing websites, if it is a ranking factor in Google's Panda update. Also whether this is in Google's wider plans for community personalisation such as the Google +1 button, if for example Mary blocks a website will it affect its ranking to her Google + community? While this would seem very harsh and cynical it is still within the realms of possiblity.
All that is certain is that standardised search engine results don't exist anymore. For more information read Matt Cutts blog entry on the announcment http://googleblog.blogspot.com/2011/03/hide-sites-to-find-more-of-what-you.html