There have been several studies showing that back links are still the most important factor for a top search engine ranking. Apparently, even back links from any website is beneficial, unless the website has been penalized by Google, the back link is advertising, or the back link was manipulated or spam. I have even seen a study showing that a footer link was helpful.
An interesting article at SEO consulting company MOZ, Can You Rank in Google Without Links? New Data Says Slim Chance, discussed MOZ’s study examining the top 50 Google search results for approximately 15,000 keywords. The article stated, “The correlation between higher rankings and the number of linking websites… …[is] actually one of the highest correlations the study found.”