1) Assad is untested. While Ben Ali was in power for 24 years, Mubarak for 30, and Gaddafi for 42 years and counting, Bashar Assad's 11 years in power do not carry similar momentum. Assad also rose to the presidency of Syria by accident after his brother Basil died in a car accident in 1994. He is an optometrist by trade. The effect of this inexperience is unclear, and may very well be the same over-compensation which cost Mubarak the Presidency. However, it may also be that Assad will delegate authority over the security services to more experienced members of the regime (or that they will out-maneuver him for control).
2) Iranian has influence in Syria. As opposed to Tunisia, Egypt, and Libya, Iran is deeply invested in Syria. Syria is a point of leverage for Iran against Israel and the United States. While Iran has been supportive of the uprisings as the "rebirth of the Islamic Revolution," this attitude may quickly change once the uprisings are on Iran's doorstep. Especially after the 2009 Green Movement protests following rigged elections in the country, Iran will not be taking any chances with its stability. As with intervention in Iraq and elsewhere, Iran will be subtle, but it will also be effective. The fact that US engagement with Syria has been slow at best will exacerbate this issue because Iran will have little competition for influence in the country.
3) The Al-Jazeera Effect will be muted. There are two reasons why. First, because Syria has very tight restrictions on freedom of the press, severely hindering al-Jazeera's ability to broadcast. Second, because violence associated with protests are ongoing in Libya, Bahrain, Oman, Yemen, and elsewhere. The eyes of the world are looking in far too many places at once for al-Jazeera to focus the same kind of attention on Syria that it focused on Egypt.