Google+ growth is accelerating. It has now gone past 62 million users and is adding about 625,000 new users per day. It is predicted to hit 400 million users by end of 2012.
Facebook needs to be concerned. Google+ is easier to use and groups can be separated so you do not need to have all posts seen by all friends. It is also easier to add links, pictures, etc. It also hosts live chats, so if you are planning an event, everyone can be online and conversing at the same time. Kind of like a free 'go-to-meeting'.