Nat Torkington writes up a good precis of Google Plus and, well, its pluses and minuses, and it’s worth a read. I agree with him especially that Circles are confusing and the ability to share with a Circle should be limited to that Circle; people in that Circle shouldn’t be able to reshare what you’ve shared with them.
He points out that Google has done the right thing in allowing you to take your data with you out of the system, unlike on Facebook. This is important. He groups this under the bad, but it should be under the good. The “free and be-advertised-to” business model is the default model, and he takes them to task for not innovating on the business model. He says “You’ll notice that none of the social networks have subscription options. Nobody says “pay me $100/yr and I’ll keep all your data private and you can have an ad-free experience.” As Kellan pointed out (on Google Plus) there is at least one service where you can pay $25 a year for exactly that, Flickr.