I disagree with the author.
I see no point in making my conversations accessable for everyone, especially if they cant actively participate in them.<p>There is no need in grouping your friends in any way, just create a circle with all your friends and those will behave the same way facebook does,at least if I got it right (by the time I got my invite it was already full).
I think there is a difference in what I want my friends and family to know about me and what people I just know but have no deeper relationship with should know.
Posting something publicly would make it accessible for everyone, twitterlike.