Excellent text that will really help you understand the concept of social bookmarking and the power it holds. The text is straight to the point and easy to read.
A very comprehensive collection of tutorials, advice, resources, tips and tools to help you use Delicious to enhance your marketing, research and other business objectives. There's a special section just for marketers.
Here are the 20 Largest Social Bookmarking Sites ranked by a combination of Inbound Links, Alexa Rank, and U.S. traffic data from Compete and Quantcast. Although no traffic metrics are completely accurate we do believe the data below to be useful for gauging relative audience size.