That was Bill Mitchell's last hurrah, and it was controversial at the time. It's been growing increasingly popular with the custom crowd, though, because the lines really are extremely nice. Dropping it and filling out the wheelwells brings out the beauty of it.
Mitchell was head of Art & Color at GM, and was quite the controversial one himself, and something of a partier and a rake. He was also responsible for the original Stingray, as well as this, which is gorgeous dead stock:
http://www.streetsideclassics.com/showcargallery.php?stock=683&location=atl&fullname=1966%20Oldsmobile%20%20Toronado