The popular comparison is that Iraq will go the way of Vietnam, a comparison that is false (and highly Americo-centric) for many reasons. However, it seems at least possible that it could become a Salvadorified narco-entrepot nexus, linked via a terrorist network to the Colombified narco-producer nexus in Afghanistan.
In fact, such an outcome has a number of recent precedents. Movements that begin with terrorist/liberationist motives and ideals often turn to drug dealing (or diamond-smuggling) to finance their efforts. As they face increasing pressure, and as the ideological-driven first generation of leadership passes from the scene, these movements often devolve into drug-dealer (or diamond-smuggling) networks pure and simple, with the old liberationist ideologies hanging on merely as a cynical legitimation exercise. Something like this has happened in various ways in places as various as Burma, Sicily, Colombia, Liberia, Peru, Afghanistan, Congo (and perhaps now in Nepal).