I have had my website listed on StumbleUpon for monthes and I have received many great reviews from the site; however, I have never had a lead from the site.. FINALLY after a few months I have a conversion from StumbleUpon... I guess it was worth the trouble after all.
I guess I got lucky.. Normally StumbleUpon just sends a lot of traffic with very few conversions.. This is a first for me.
Stumble is easy to get traffic compared to Digg. Digg traffic converts well compared to stumble! I'm also making atleast 1 sale($60/sale) per month just with stumble!