Social bookmarking sites allow websurfers to save, catalog, and share interesting pages they find online. The Sociable plugin appends links for your readers to use those sites to the end of each of your blog’s posts, increasing your potential audience. more info here http://blog.errorforum.com/social-bookmark/
Nice knowledge shared, Well dont know about you people, however if anyone of you would intted in paid bookmarking can contact me .. anywayz its better to share and live the things according to it, as we exist because of sharing the good information.
I would recommend Gregarious (http://dev.lipidity.com/feature/wp-plugin-gregarious) not only because its got more features (including the Digg button), but because it's a lot cleaner due to the implementation of Alex King's Share This. Of course, I am biased since I'm writing the plugin...