I was reading through some articles on problogger.net and came across this article explaining how he has seen stumbleupon bringing in more traffic over a period of time than does digg. Have you guys had similar results? http://www.problogger.net/archives/2007/07/06/why-stumbleupon-sends-more-traffic-than-digg/
Not sure about this one, I think that SU might deliver more traffic over a long period of time but digg brings in far more at once, often crashing servers. I got in featured at stumbleupon and only got around 300 visitors from it while at digg you get far more, but with SU you get visitors using the Stumble button.
i prefer digg traffic because StumbleUpon traffic mostly looks like ghost traffic . they are coming and going away at the same second
Indeed digg traffic is more likely related, instead SU is just a flood of traffic from un-targeted visitors. If you would pay attention the SU traffic not only that vanishes much faster but also the bounce rate of visitors (how fast they leave your site) is way much bigger.