Google is getting into Facebook territory now since they have launched Google+ comments for Blogger based websites. Maybe in the future they might expand and allow platforms other than Blogger or WordPress to integrate Google+ comments too.
The new comments feature can be activated from the Blogger Dashboard and it is a purely opt-in model. Those commenting on the blog will have the option to comment publicly or privately for their Google+ circles. While reading comments, users can choose to view all comments, just the top ones or only the comments made by people in their circles.
Google+ users will love this new feature. Older comments on any blog will continue to be displayed in the new widget.