I have not been invited yet to Google +, although frustratingly, others have invited me to join. But Google had to shut down that option after too many people rushed to sign up. Check out Google's demonstration video for Google +. If you're like me, Facebook has become this huge mass of disparate folks ranging from close family and friends to work colleagues and acquaintances and people I don't even know. Twitter is easier--anyone can follow me, and I can select who I follow. But when one group starts live-tweeting a movie or football game--that could be done as a Google + hangout without either imposing it on disinterested Twitter followers or asking people to temporarily unfollow you.
Google + makes it easy to drag people into different groups or circles, hang out with a group at one time, or huddle by choosing to meet at a given place. The issue for me is the time it will take to create yet another world, again. My gmail contacts are a mess--I rely on search. My email groups are way out of date. Maybe it's time to get that going.