Opposition Movement Strength
Probably the most critical variable in determining revolution success is the strength of the opposition movement. A strong movement includes many organizations with different ideas who include a wide diversity of members. These organizations should already exist and have experience. They should be united in a loose coalition to overthrow the government.
Outside of regular mentions of the Muslim Brotherhood (and occasional mentions of the Egyptian April 6th Youth Movement), I haven't see mentions in the media of what organizations are behind the revolutions.
It is hard to quantify the strength of these movements. You can at least measure whether there is a recent history of protests, for instance Egypt has had a protest movement for several years (and Egypt starting using Facebook for activism in 2008).
You need these organizations to avoid having a violent revolution that is two factions of the military fighting each other, or the people fighting the military (with violence).
It is possible that a lack of these organizations which is allowing Gadaffi to kill many people, without losing the support of the military.
Muslim Brotherhood - Wikipedia
Egypt
Players in Egypt's Opposition Movement
Kefaya - Egyptian Movement for Change. Played a major role in 2005.
April 6th Youth Movement - started in the Spring 2008 as a Facebook group to support a textile workers strike and developed larger reform goals.
Hisham Mubarak Law Center - legal support for human rights
National Association for Change - started by Mohamed El Baradei
Egyptian 2005 Presidential Election - allowed two opposition candidates to stand, but it was not fair.
List of political parties in Egypt - historical and current.