I had someone ask me a great question today about the difference between Google Plus and Google Groups, especially with regard to use in the classroom. My initial response was that they are quite similar in what they provide, however, they do differ in their interactivity and functionality. As you may suspect, there are plusses and minuses to both, but Sharon Huston created a great slideshow that does a great job at comparing/contrasting these two services. Check it out!
Sharing with Your Class -- Google Groups and Google Communities