Peter Da Vanzo poses a question on SEOBook asking if social media marketing is a waste of time. In it, he adds a few qualifiers including traffic (is the traffic to your page to see a monkey riding a bicycle worth it?), an uncontrolled message, a concern about the ability not to measure branding, the level of interaction isn't clear, it takes time, it's stupid and is a useless distraction, and it's difficult to scale.
This all may be true to an extent. EGOL recounts his own experience being Dugg: when the page was submitted to Digg, it had no inbound links. Within a few weeks, though, it had several hundred. Three years later, it's still on the top of the Google SERPs.
That said, it's not completely a waste of time.
I should add that this industry is very focused on Social Media Marketing as getting Dugg on the front page. That's not all there is to SMM.
One important thing to note, as shared by forum member glyn:
The thing with Social Media is the moment you get too specific with your advertising you scare the user base away.
Forum discussion continues at Crea8site Forums.