What the hell are they smoking over there at SU?
"Since updating the product in late 2011, we have been gathering feedback from our users and partners. Overall, the response has been positive as both users and partners have found the redesign an easier way to discover and share great content."
According to the following article, it appears they might be acknowledging some level of fail since they are doing away with the whole channel concept.
Stumbleupon’s redesign falls flat [Update] - CBS News)