I'm not challenging, just curious. It seems to be pretty widely accepted that news aggregators have, in general, deteriorated; particularly digg & reddit, too new to hackernews to have an opinion. I hadn't noticed the same phenomenon with stumble ...
I actually quit using stumbleupon but I had heard that it wasn't getting updates that frequently and that their growth rate has been slowing down a lot. Doing a quick search I didn't see anyone stating bad things about it, so I don't have anything to point to but I recall hearing it discussed.
Still doesn't interest me that much though, rarely use digg - just every now and then when I'm bored.