I just read an article entitled "31 Great Ways Universities are Using Google+" and was thinking that K12 could, and should, do many of these. Each way has a link to more information and ideas for that topic.
Google+ is an excellent resource for education, educators and students. It allows for communication, collaboration, sharing and so much more.
Some of the ideas from the article that I think K12 can also use include online meetings, online help sessions with students, increased and improved communication among staff, faculty, admin, students, and parents, student feedback, extracurricular activity communication and collaboration, class conversations, posting of student materials and resources.
Check out the article and see some great ideas for using Google+ in Education.
Google for Educators Resources, tips, links, lesson ideas, help, and more
Google Plus - tips for using in education, facts and data infographic
Google+ - More Reasons its great for Education
Google+ and Google+ Pages - great for educators and schools
10 Ways to Use Google Plus in the Classroom
Teaching with Google Plus - tips and resources
Twitter, Google Plus, Facebook - a nice comparison
Google Plus now open to Teens, with safety features