They're not out yet. I'm waiting eagerly to see what degree of openness they offer. My bet is that in this first release they'll offer a compromise between openness and Google's desire to keep Google+ a service that works well for its users.
To me, that's the biggest challenge in an open interoperable social layer: preserving a good user experience.
To me, that's the biggest challenge in an open interoperable social layer: preserving a good user experience.