A feature previously only available as an extension for Chrome, users with a Google Account can now maintain their own, personal blacklist of sites whose search results aren't useful.
The original entry about this release on the Google blog tells the story, and you can click the following link to actually access your very own Manage Blocked Sites screen (assuming you're signed in to your Google account).
I mainly use Google, Bing, and Ask for my searches, but now Google is in my top spot solely for this feature. Too often I've submitted a query to a search engine only to be bombarded by useless results consisting of anything from advertising to porn to advertising about porn to malware, and habitually I'd just click the third or fourth page of results in the hope that I'd find some worthwhile content. Now I can shape my search results by eliminating much of the fluff, which translates into much more productive searches.
Creators of fluff are on notice:
"Sites will be blocked only for you, but Google may use everyone's blocking information to improve the ranking of search results overall."
Content is king, as the saying goes, and this is one big step in helping us mere users leverage the system by enabling us to trim away the fluff as we find it.
Well played, Google!