Remember Google's search feature that let you block websites? The one that launched in March 2011, expanded globally in September 2011, and then vanished and became useless by January 2012? It's now officially discontinued, according to this page.
"The Blocked Sites feature is no longer available," according to Google. "To block particular sites from your search results, we recommend the Personal Blocklist Chrome extension from Google. You may also download your existing blocked sites list as a text file."
The Blocked Sites feature was basically killed at the same time Google Search Plus Your World launched. Before that, users would see a note underneath or next to a URL ("Block all example.com results") after clicking the back button and returning to Google’s search results page:
After you hid a search result, you'd see this message, telling you how to manage your blocked sites:
After Blocked Sites launched, Google said it was using data from this feature, as well the Chrome Personal Blocklist extension, as a ranking signal as part of the Panda algorithm.