In a recent study conducted by Forrester, it was discovered that Google Plus is definitely worth including into the marketer's daily mix:
Brands’ Google Plus posts generated nearly as much engagement per follower as their Facebook posts — and almost twice as much engagement per follower as their Twitter posts.
Even for those who are "in the know" about the benefits of Plus, many have difficulty learning how to use Plus effectively. In this instructographic, we discuss an overview of how to use Google Plus for marketing, including a daily recipe for Google Plus success.
A comprehensive guide to marketing on Google Plus is a good read alongside this infographic.