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Social Bookmarks: Not for Bloggers Only by Heidi Cohen
Many bloggers treat social bookmarking sites such as StumbleUpon as traffic generators, which they can be. However there is a lot more to social bookmarking than just traffic.
One of the biggest advantages in having a post bookmarked is its ability to send the search engine bot to your site to read and index the post that has been indexed. This can often speed up the indexing process by hours, if not days, depending on the frequency of their visits.
More importantly, some social bookmarking sites create back links to the post, thereby increasing the number of back links coming in to your blog. The back link is a deep link to the post itself as well, not just the front page.
Jill Catrina