Ignore Google+ at your peril, it is currently running neck and neck with Twitter in terms of registered members. It has rapidly outrun LinkedIn and is catching up at a phenomenal pace on Facebook, although Twitter is said to be growing faster!
Since Google link all their activities, its Youtube, Google Maps, etc, they are creating a network of users that is interconnected. Google will prioritise all content that has been +1'd or shared on their circles (part of Google+).
Google now use your social relationships in determining what content is relevant to you. As I say, ignore at your peril!
Author: Matt Connaire
