A few more comments to add to this discussion...
In connection with the statistical data I submitted, I was obviously misinformed. The data came from a respected Ukrainian Orthodox (U.S.A.) priest, perhaps he was referring to financially contributing supporters of the church or financial contributions to the church---it was 15 years ago when I had this conversation; however, I've never before seen a 150 million population statistic for the Church of Russia, 100 million seems to be more commonly used in my experience. (100 million was the statistic commonly used, in my experience, for the Russian Church populous prior to the Bolshevik Revolution, too.)
Regarding the assertion that there is one Orthodox Church, of course, no doubt. Fr. John Meyendorff had written that the ethnic appellations, Greek, Serbian, Romanian, etc., are the result of the 16th to 17th century nationalist movements in the Ottoman Empire, which to some extent, operated within the churches. He made the point, if, in any of the commonly spoken languages of the Ottoman Empire, an Eastern Orthodox Christian is asked, "To which religion do you belong?" the answer was "I am Orthodox," not "I am Greek Orthodox," etc. I've noticed on facebook, when Greeks (from Greece) post their religion, they put "Christian Orthodox."
Regarding the Ukrainian Church divisions, there's another topic on "oc.net" that demonstrated that there are many separated churches therein, not just the two most prominent. Also, in the mid-1990's when Patriarch Bartholomew was engaged in discussions with the two prominent separated Ukrainian Churches, he told them to resolve their differences, and return to discussions with the Ecumenical Patriarchate as an administratively united church.