I was doing some stumbling this morning and came across a really funny breakdown of the major social bookmarking / social networking websites.
Here’s a little clip of their explanation from the page I found:
“Would you like to make connections for business relationships or communicate to your legions of followers that you will be ‘AFK’ for [...]

Today is a video day. So here’s a video about how StumbleUpon can skyrocket your traffic stats.

yahooBuzzArticleHeadline = “StumbleUpon Traffic Blasting”;

http://businessblogs.us/blog/social-bookmarking/442/stumbleupon-traffic-blasting.html