Google introduces "Personal Blocklist" (Chrome extension)

The personal blocklist extension will transmit to Google the patterns that you choose to block. When you choose to block or unblock a pattern, the extension will also transmit to Google the URL of the web page on which the blocked or unblocked search results are displayed

https://chrome.google.com/webstore/detail/nolijncfnkgaikbjbdaogikpmpbdcdef