stumbleupon is a resource that sends random "requested" traffic to your website. Bookmarking is more like PR when you have an article you place it on a site where people can find your site from your catchy headline. Like digg.com, reddit.com, furl.com... matter of fact here is a good article: http://searchengineland.com/071120-144401.php
Hi There, There are lots of websites for the social book marking, and its your good step to go for the social book marking, we don't need PR, we want traffic for our websites and social book marking site really help to get and higher rank in SERP's. click on link below and find out the best social book marking sites on web. 100 way to promote your website Classifieds are as much as important as social book marking, and one of the best reason to choose classifieds for advertising your site that some of classifieds sites are not having nofollow links, so it could be counted in your back link weight also. Free classified list Thanks and Regards, Chaitanya Patel.
stumbling is easy, just get a firefix/browser plugin and stumble til your finger turn blue. But their traffic is (sadly) very low quality, hardly converts.
I've seen a few e-books out there that tell you how to use the Social bookmark sites to your advantage. The information is not anything you can't find for free on the web, but at least they put it in one place and spoon feed you what you want to know.
Stumbleupon.com is waste of your time and effort. It will not bring you any relevant traffic just quick browsers.
what kind of help you want from here...Do you want social bookmarking site list OR want to know more about it OR its benefit...
Stompernet has just released a good free report that explains some of your questions. You could download it for free.