Oh I remember, when I made my first site few years ago, site got suspended because of hordes of crazy Stumblers that came all at once on my site, mothafuckers destroyed my project I was working for a month.
I should probably pick paid hosting [hmmm]
Whatever, few years ago, SU was great for getting tons of traffic, just like Digg. I've tried Pinterest, and, logic behind it, doesnt allow such traffic.
I love Pinterest but it is highly addictive. I have to use a timer or else the 5 minutes I had planned to spend on there ends up being 2 hours. At that point, since all my pins for the week are scheduled, I just find cool images, comment on people's pins and boards, and reach out to other like minded individuals. It's well worth a try, the learning curve is very small so it wont' take you much time to figure out. Also, try SEOClerks, they have excellent services out there regarding Pinterest followers!
Stumbleupon is quite a veteran in the world wide web so comparing it to pinterest is not really ideal. But right now I am leaning into pinterest more although I am still clueless on how I can utilize it for traffic. Will look down into it real soon.