When it comes to link building, quality is what matters most. I don’t buy the “any link is a good link” notion. Your time is limited and the last thing you want is wasting it to get useless backlinks.
Social bookmarks if used incorrectly are ones of those kinds of links that border with useless. What good is a link from a page with potentially 100s of outgoing links or from a page buried deep deep down the hierarchy of the site? Your time is better spent getting quality links than spamming social bookmarking sites.
With that said, there’s a lot of potential in social bookmarks, in its viral aspect. Bookmarks are social because they are viral. An interesting link can be spread through out the site and beyond like a virus and result in traffic as well as backlinks most of which happens automatically.
The trick is to tip a bookmark to go viral. It’s not an easy task, but bookmarking your most interesting pages is a good start. Keep in mind the demographics of the sites you submit the links to, research what kind of links are most popular and go to the top. As a rule of thumb, bookmarking a “proxy” (ex. youtube video, etc.) site rather than your own gets more attention as they are known sites with authority (as opposed your unknown site).

