This is why I need to follow our analytics more closely - I was checking our Google Analytics data for referrals from third party sites and realized Stumbleupon was no longer in the top 10 summary. This was strange because Stumbleupon used to be our top referrer!
At first I chalked it up to the changing fads of the web; maybe everyone moved on to Pinterest and Tumblr and whatevr. But then I isolated the Stumbleupon graph and did a long-term view. Last October Stumbleupon was sending us 80,000 visitors PER DAY. Then in mid-may 2012, they simply shut it down... Less than 1,000 referrals per day.
This is really chilling, that was a considerable amount of our traffic! Also those daily visitors could have become repeat visitors, long-term fans, could pass links to friends, etc. This change had a real impact on NG and I never noticed it.
I couldn't find an email for stumbleupon so I've just Tweeted them so far. I read some stuff about how they blacklist sites that abuse their system but we've NEVER abused their system or tried doing ANYTHING to improve our results there.
So it's like WOW, it sure would be nice to get that traffic back! If anyone knows anyone at Stumbleupon, please ask them what's up. Hopefully this post can get their attention and they'll look into the matter. If anyone has any further info on their policies, let me know! Maybe too many people were stumbling on the wrong kind of submissions.
UPDATE: Some bad ads had come through our ad company for a few days in May and in that moment someone reported it to Stumbleupon and we were indeed blacklisted. They are reviewing the site now and we may soon return to Stumbleupon! Damn I wish I had noticed this sooner.
UPDATE 2: We are now back on Stumbleupon! Hopefully that graph will pop back up.