I now think it's impossible to deny that the single most important factor shaping the Arab regional dynamic is a sectarian divide, not between Sunnis and Shia, but between Sunnis and everybody else. On the sidelines are also significant divisions between Arabs and ethnic minorities such as Kurds or Berbers, but it is the sectarian split that is the real dividing line these days. This new sectarian consciousness has greatly assisted the rise of Turkey as a regional power, strongly aligned with Arab Sunnis, at least for the moment.
Iran is probably the biggest single loser in the regional realignment so far, and the mainstay of many governments trying to blame unrest on "foreign powers" (along with al Qaeda, Israel, the United States, Saudi Arabia, Qatar and Turkey, depending on which government is making excuses). However, an Arab world divided along sectarian lines will continue to provide potential openings for Iran in Shia and other non-Sunni areas, even where they have had little or no influence in the past.
The emerging sectarian narrative threatens to rip apart many Arab societies, and indeed the Arab world in general. More than military dictatorships or violent organizations that may seek to exploit these tensions, the illusions that Sunni Arabs across the region are seeking to impose a new and repressive order on non-Sunni Arabs, or that non-Sunni Arabs are subversive elements or disloyal agents of Iran or other foreign powers, pose the gravest threat to a better future in the Middle East.