The best example is the March Al Sadr uprising in Baghdad, where large street protests began peacefully and then turned into an organized guerilla warfare front. Najaf was similar.
The protests basically allowed the guerillas to cross the area of vulnerability and gain strategic positions so they could emplace weapons and consolidate territory gains.
They were later bombed into the stone age, but the tactics they used were solid.
Combine these tactics with thousands of people who have been to prison and converted to Islam , deep hatred of America, and some knowledge of tactics, and it could be the beginning of a logistics and intelligence network. Add a few ME infiltrators who are dedicated to insurrection, and we would have a problem.
Ahhhh yes. I'd forgotten the OZ scenario (like the HBO series). The recruits to the cause from the population of Americas toughest prisons. You're correct. Especially those few who might have former military experience or more probably those who have gang affiliations might well pose a problem. Especially if the AQ's promise them right to any "spoils of war" they may come across during the Jihad.