I use both social networking and social bookmarking for all of my websites and some days I recieve good amounts of traffic so it must be working, plus it is very easy to target relevant traffic on Facebook.
Have you signed up for a free account on
OnlyWire.com which allows you to sign up to 50 social bookmarking sites and submit to them all automatically it really is a great tool. (You get 300 submissions free and can upgrade from as little as $10) Well worth taking a look at)