Google+
Google's social network,
Google+, had 170 million users as of May of this year, according to Go-Gulf.com. One of the Google+'s early differentiators was its Circles capability, where users could group contacts in categories, thereby logically separating their business and personal interactions. Facebook has increased its ability in this area, but, as with many things Facebook, it can be complicated to do so. Google's Hangouts feature has also been a big draw, as has the clean (i.e., uncluttered by ads) interface and integration with Google's overall platform.
Further Reading
How To Keep Your Brand Liked
Google+ Satisfies While Facebook Slides
Twitter Tweaks Tweet Search
9 Facebook Buttons We Want To See
LinkedIn Password Breach: 9 Facts Key To Lawsuit
Early Twitter Team Member Dishes On Service's Origins
Pinterest: Why Your Company Should Take An Interest