I don't think there should be any "?" in the title of this thread. Reality is that users now would rather visit your social network fan page than your site so you have to be where your users are, not the opposite.
Social networks such as facebook and twitter becomes one of the top online venue to market any service and products because of its exposure to the public.
Marketing through social network ...donno much..but traffic would be awesome/...converting traffic to buyers is all matters
Facebook and Twitter are good social networking sites which helps in getting traffic and unique visits .