From the Facebook Newsroom:
To reduce the number of these types of posts, News Feed will take into account when many people flag a post as false. News Feed will also take into account when many people choose to delete posts. This means a post with a link to an article that many people have reported as a hoax or chosen to delete will get reduced distribution in News Feed. This update will apply to posts including links, photos, videos and status updates.
Posts that receive lots of reports will be annotated with a message warning people that many others on Facebook have reported it.
This change appears to be focused primarily on news sites that pump out hoaxes regularly, so your paranoid uncle will still be able to make ignorant comments on Onion articles at least!