I have made it explicit that I automatically unrecommend articles by authors who I feel who have engaged in dishonesty and hyperbole in the past; examples of such are Glenn Greenwald and Jane Hamsher. If I have ever carried out the process for certain DU authors, it has been a long time since I have done so, because I don't recall any. As the topic has arisen here in Ask the Administrators, I would like to offer a defense of this practice.
If an author writes a dishonest article, and it is called out as dishonest and left at that, there is really no disincentive to writing another dishonest article. They can always keep trying to foist lies into the public debate, knowing that if they fail at it, the worst that can happen is that it does not work, and the best that can happen is that it is believed. With these terms, they can simply try again, as many times as they'd like.
I put certain authors on automatic unrecommend to give them disincentive to be dishonest with every article they write, and thus honest all the time. I think that I have announced it every time that I've done it.
I will add that I actually don't object to patterned or sustained campaigns of unrecommending certain posters myself, despite possibly being the most consistently unrecommended poster in the history of DU. I don't think there's any way of telling whether or not it's being done with ill intent or not, and the measures that would have to be employed to weed it out would possibly be restrictive. Indeed, I have only complained about the practice in very light terms, such as the fact that my appeal for more bone marrow donors was unrecommended below zero:
http://www.democraticunderground.com/discuss/duboard.php?az=show_topic&forum=389&topic_id=7528170