Stumble upon is superb traffic generating website, i used it for my website for the sake of social book marking and shared it with my friends on the same network, as a result almost hundreds of traffic was the part of my analytics. i would really assure you people to use this network too.
Stumble upon one of the best sites to generate the traffic if one has the passions to work on this site. it is really a good site which can bring you a lot of traffic than the top most social networking site Facebook or twitter
I don't think so. I have an account on Stumble Upon but I'm not currently updating it. Maybe you can try it.