I will say very important.
Trust, Authority, Relevance, Age....
These factors are all imortant when building quality backlins.
But every link is counting, but not treated equal.
So backlink from SB sites will not have significant role in SERP's, but link from old and trusted, authoruty domain in that niche with right anchor will have great impact on your rankings. So try to focus your energy to build relevant and quality links, but always try to mix up low quality links with this super quality ones especialy if your site si new or have few backlinks.
Nemanja