Some social bookmark sites like Propeller.com pass on link juice, while some use the NoFollow attribute. But do not let the use of NoFollow fool you, the search engines are looking beyond the incoming links from social bookmarking sites to gauge their value to their search indexes. The external metadata compiled via user generated descriptions, tags, titles and categorization is incredibly valued by the search engines, as in the same philosophy as anchored backlinks, descriptive content about a web site defined by the users of that site who are not associated with the marketing or coding of that site, can be extremely powerful in gauging the importance and relevance of the content and tags which are used on that site.

Bookmarks show how a site is perceived, and when these sites allow voting,