Given the predisposition of RB to defend the Roman position, allow me to rephrase his question to: "How many of the "apostolic" sees still remain in (or are back to) their original place of establishment/founding?
Let us further assume that we refer to those apostolic sees as the original 5 Patriarchates of Rome, Constantinople, Antioch, Alexandria, and Jerusalem.
Within these parameters, only the Patriarchate of Antioch seems to be displaced for the reasons already mentioned, with the Patriarchate of Constantinople in danger of being smoked out of Istanbul.
The Patriarchate of Jerusalem is, of course, presently under the strictures of the Israeli government and the Patriarchate of Alexandira is slowly being engulfed by Islam.
As a vibrant, alive, and freely "functioning" Patriarchal See, central to the governance of the territorial reaches of the Church/Churches under its provenance, arguably only the See of Rome is extant to this day, which leads me to reference made by RB on the current signification of the "Holy See."
In modern parlance, the "Holy See" refers to none other than the Roman See. Alternately, it refers to the Vatican City State, de facto et de jure, as enshrined by international law and comity and recognized by ALL members of the United Nations. Thus, plenipotentiaries appointed by individual countries to the Vatican present their "letters of credence" to the Pope as ambassadors to the Holy See.
Feel free to disagree.