In the recent Iraq War, the US had a number of war aims, including the institution of a subordinate and model neoliberal regime that would secure energy resources and the establishment of a network of permanent bases to house American forces in a strategic location. The resistance was fierce: In 2005, suicide bombings hit a record of 478 separate attacks. This insurgency caused the US to progressively lose desired outcomes on point after point - accelerating elections, largely losing the elections, energy market diversification, the inclusion of anti-occupation forces in government, the arming of independent militia, inability to drawdown troops, the need for conversion to a contractor army and many others. The insurgency imposed immense costs on the Americans - estimated to run into the trillions of dollars and at the expense of many thousands of lives. The insurgency was unable, as it stands, to consistently assert its own political demands beyond the mere raising of costs and explosion of war aims for the Americans. Importantly, though, it gives a sense of the stakes involved in politics: Each side committed immense human and economic resources to the effort to shape strategic outcomes of the country.
The violent and more spectacular side of the Iraq insurgency was certainly important in defining events, but it was the largely latent power of assertiveness of the population that was decisive in largely derailing the occupation. American resistance to local popular power was fought with massive crowds of protestors, despite extreme personal danger to these crowds, and it was this political activism that convinced the US that it could never hope to sustain a puppet government with large permanent bases. This wasn't simply non-violent - often the crowds were supporters of militia leaders like Muqtada al-Sadr. The latter's resistance movement now controls a critical share of votes within the Iraqi legislature.
The world-historical consequence of the Occupy movement needs to be put in this perspective. This is the same world and involves one of the same powers. So far, the Occupy movement has involved a tiny minority of Americans, and at very little expense for these people. There are attacks with irritants on protestors, but most violence has been one-sided and limited. Importantly, what are the changes in business-as-usual that this movement seeks to put into place?
I believe in something I call "business plan politics." That is, you need to have a narrative about how your politics will change the course of events. You need a credible strategy. You can't typically show up to a bank for a small business loan without at least the semblance of a strategy to convert the loan into a profitable enterprise so it can be repaid. But people spend a lot of time on their politics without considering how their micropolitical activity will translate into social change. This is why revolution must be approached as essentially a scientific activity - what inputs lead to what outputs, and so on. You need a credible way to translate vague ideas about a future society into tangible results. There's nothing of that in the Occupy movement yet.
Total expenses of the security state in the US total near a trillion dollars a year. Overthrowing such a state and introducing new social relations will not happen because of occupied parks. It will come because millions of people choose a new road and thousands of people give their lives for it. These are the stakes. History advances by the bad side - you have to wrench small advances out of incredible expenditures. The struggle against capitalism has cost countless millions of lives across centuries. The impossible happens, but one must plan for it!