You can now block "content farms" with a Chrome extension.
Content farms are websites that just re-publish information from useful sites like stackexchange.com, and fill the rest of their site with ads. When you search the web, you end up finding their site first, and they get credit for people seeing their ads.
Some sites like (yeah I'm not naming sites, they don't need more publicity) come up near the top in a search and it’s a pay site – they expose the questions but demand payment for the responses from members (even though the answer is still exposed at the bottom of 12 pages of ads).
I found a list of content farms (although some may just be annoying sites).
Whatever you block is reported to Google and supposedly they will take them into consideration for their search rankings.