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There are two main contenders in the social bookmarking sphere, delicious.com and StumbleUpon. While StumbleUpon is arguably not a bookmarking service at its core—instead, it’s a content discovery engine—it contains many of the same elements seen in social bookmarking services, and since it can be and often is used as a bookmarking tool, we will explore it further in this chapter. Yahoo!-owned delicious.com, on the other hand, is by far the leading social bookmarking service on the Internet. We will look at how to use these services for storing bookmarks, retrieving bookmarks, finding new content, and networking.
A third site, Diigo, is becoming increasingly popular for social bookmarking. Like delicious.com, it is a social bookmarking tool but with a lot more feature enhancements that are not available in the widespread delicious.com application.