How Important are Social Media Backlinks?

I talked with my mentor who does coaching for local SEO consultants. He gave us a whole speech on how ever since Hummingbird update, Facebook and Twitter backlinks are having a growing importance on rankings.
I see a lot of people obsessing over PR this, PR that, but make sure at least 5% of your backlinks come from social media; especially Facebook and Twitter.
Tumblr is 3rd in importance.

How have you used social media in your backlinks?

Poster :
Mike Park