Back in the old SEO days, social bookmarking was one of the most effective methods of link-building. It's still effective now but has to be done in a effective way after the recent Panda and Penguin updates from Google. Frankly speaking, things don't work as they used to, so you have to be careful while carrying out these stuffs now a days.
Don't go for 100's of social bookmarking sites, just go for a few which are high in page rank because pages of high PR sites gets indexed faster and so does your links submitted to these sites. Try to use different title, description and other fields for each of your submission to remain on the safe side as submitting the same details (even to different sites) over and over again really looks loony and spammy. The final advice is to use different usernames on different social bookmarking sites as this would leave no footprint that you are some way or the other trying to manipulate by pushing your links to get into the search engine result pages.
Social bookmarking is a method for web users to store, organize, search, and manage bookmarks of web pages on the Internet with the help of tags or keywords on sites such as Digg or Del.icio.us. This helps you in accessing bookmarks from any computer with online access. These bookmarks can either be public or private. If public, your favorite bookmarks visible for others to view and follow as well, hence the social networking aspect.
Yes, it is Social Bookmarking is very Effective. It creates backlinks. And for generating traffic in your site, it is the best way. But for more backlinks for your website, you should submit your site into high PR Social Bookmarking websites. Like Reddit,StumbleUpon,Digg & so on.
I would like to add some few ideas to this post as I am feeling that doing so would make it a bit more clear. Social bookmarking is part of your link building process or strategy. If you can target some good high PR dofollow social bookmarking sites and then submit your links there, it's better for your site. Why?
Because social bookmarking sites with higher pagerank and alexa are seriously quite often visited by the Google bot and pages submitted one these sites get indexed very fast. So your submitted link will also get indexed faster in that sense.
The more links you can get from these authority sites, better the chances that your site's pagerank will also increase. So keep doing it effective and don't hurry, bookmark your links naturally.
Submit only on high authority sites like Reddit, delicious, stumble-upon and digg. Don't submit on other websites. I have submitted on many websites before the google updates and got hit very bad. Most of the sites are down and not able to remove any of links. Will Google consider these sites as back links to my website, even the site is down?
The social bookmarks that you submit online can also get listed in the search results based on how well you make the bookmarks. If the descriptions and the titles you create are keyword rich your bookmarks will be listed in the search results.