I don`t really thing social media could help SEO, because most social media websites have nofollow links, but social media could get you a bunch of traffic if you have a good profile, you`re active, make a lot of friends and this stuff
Social media can be used for both link building / help faster indexing / traffics driven. However, the main purpose of social bookmark should be traffics driven over link building or seo solely purpose. Links from social bookmark won't last long, thus not a much weight to no weight since most of them have been attached with "nofollow" attribute. I would recommend you use social bookmark and link bait strategy to attract a huge spikes of traffics for both short and long term period, depend on your audience type and niche. Here is a good sources for link bait building and strategy Link Bait SEO Advice: linkbait and linkbaiting How to make use of link baiting and viral marketing in search ...
Hey, Right Now Social Media plays very vital role in ranking and also in traffic, so you social media at the view point of traffic. so you will get good back link and also good page rank also.
Hello Friend , In these days social media optimization is going on according to social media optimization we can get good traffic .
twitter is the only social media site that will bring in some real traffic. If you can build up a huge list of followers you have a good chance of gaining more traffic.