Drawback: Have '+' Will Travel
Keeping tabs on Google+ might be a great feature for playtime, but having a notification icon incrementing in real time could prove annoying if you need to work. The navigation bar goes almost everywhere with you in the Googleverse, including Google Docs. It would be better to have an option that lets you mute Google+ notifications whenever you open a file in Google Docs.
Drawback: E-mail notifications
E-mail notifications drive me nuts; I get too many of them already. By default Google+ was adding to the noise by sending me an alert for what felt like everything that happened on Google+. Turning them off was easy enough, all I had to do was go into my settings and the first thing I saw was a list of all my active e-mail notifications. I just deselected the notifications I didn't need and I was ready to go.
Another strange thing about e-mail is that Google lets you add contacts who aren't using Google+ yet. Let's say I added my sister and father, who aren't on Google+, to my family circle. Every time I shared something with that circle, they would get an e-mail update about my activity on Google+. That seems a little on the spammy side to me. Although, Google makes it very clear that you will be sharing content with someone who can only participate via e-mail.
While Google+ is focused on sharing and chatting with people right now, the service has a lot of potential for new features. Adding a Wave-like capability that lets multiple users collaborate on a document or project would be a nice addition. Some sort of playlist sharing feature would also be nice if Google can ever figure out licensing deals with the major record labels. But that's just speculation about what the future might bring; for now Google+ is all about content sharing and once it becomes publicly available it is well worth checking out.