It isn't yet clear how much success Google+ will have. But the fact that Google has invested heavily in what has to be called a new social initiative tells you all you need to know about the growing importance of social networks in media, and as media.
Up to this point, search algorithms have been built around pages and links. Google never discloses its actual algorithms, but the "PageRank" formula uses the number, type, and reputation of other pages that link to any given site as a major ranking factor. These days, though, the explosion of social networks has had an effect.
Today, far more status updates, photos, videos and other social flotsam and jetsam are published and shared than fully formed Web pages. That’s because content creation is now about "small stuff," rather than "big stuff." The popularity of such "micro" bits of content is that there now is a need to index lots more "personal" content, compared to commercial, professional or other more traditional content sources and sites.
That doesn't mean traditional sites have to be abandoned for Twitter streams. It does mean that it makes a difference whether content gets re-tweeted, "like" or otherwise shared. Google, for example, now incorporates Twitter data into Google results.
Specifically, tweets and mentions of your published content receives has a material impact on how Google ranks your sites, pages, posts and stories.
The issue for content marketing is that social sharing is becoming a more important SEO requirement.