If you go back and read Habermas, who coined the term "public sphere" (which was what was used in the article), the first public spheres were private salons, coffee houses, and cafes. The discourse of the public sphere was also carried out in the (privately owned) media of the time (newspapers and pamphlets).
http://en.wikipedia.org/wiki/Public_sphere#J.C3.BCrgen_Haber...
Another (less readable) book on the subject is Badlands of Modernity, which discusses distinct spaces in which social orders are changed. The Palais-Royale in Paris, the private residence of Louis Philippe II d'Orléans, was one such site in which the ideals of the French Revolution were acted out before the revolution itself.
http://books.google.com/books?id=B0D0EOJoyMsC
http://en.wikipedia.org/wiki/Palais-Royal#The_Palais_Under_t...
Private spaces are just as capable of being inclusive, liberal, open commons as public spaces. Indeed, in times of oppressive government, it is private spaces that become the refuge of the remnants of openness. This is one reason why liberal theorists from the Enlightenment era regarded the ownership of private property as a right essential to the maintenance of liberty.