Egypt is huge, but relatively homogeneous. Except for the Coptic Christian community, it is overwhelmingly Sunni Muslim. That saved the popular democratic movement from becoming an ethnic wedge issue.
But elsewhere in the Middle East, deep ethno-religious differences likely will lead to different outcomes. Take Bahrain, where a Sunni minority holds power over a Shiite majority, many of whom are ethnically tied to Iran. The political sphere is relatively open already, but it is a monarchy, which irks the young and liberal. At the same time, fundamentalists have made political gains in recent elections.
Ethnic complexities exist throughout the Gulf, including in Saudi Arabia. Iraq and Syria also have significant ethnic divisions. Lebanon, of course, is a classic case of this, a tiny nation divided among Sunni, Shiite, Maronite Christian, Druze, and other groups.
Then there's Iran. Democracy advocates have faced a fierce response from the clergy-dominated government. Both sides are largely Shiite. Both are trying to claim Egypt as supporting their cause.
Bottom line: Ethnic differences mean that every country in the Middle East will be affected by the Egyptian revolution in a different way.