StumbleUpon Statistics: Traffic Down 53 Percent Since JulyNovember 6, 2012 4:11 pm
Well, as new content discovery mechanisms emerge, existing ones face challenges. We had spotted stumblepon stats in the past – we spotted a stat today that SU traffic is down by more than half in the last 4 months (Source)
Again,this could just be a blip in the overall scheme of things for StumbleUpon. We never know.