Digg is a social networking site that allows people and web surfers to share websites, blog posts, and articles they find interesting, shocking, humorous, etc. Digg and public libraries are similar because they both organize information in ways that are easily accessible to the reader or web browser. Digg is also similar to public libraries in that it makes popular information easily accessible to users. Public libraries also strive to make popular best sellers or information resources available to the public, and don't just collect information indiscriminately of population's demographic wants and needs.
Digg is similar but has a much broader demographic and so it's sites appeal to more people than a local public library would.

Libraries can use Digg or similar sites by adding a button to their blog entries or website that allow web surfers to "Digg This!" This would add traffic to the blog or website as well because more people would be aware of its existence.