Following an outbreak of zombies, the United States would quickly put into place a commission to research the validity of such an outbreak. Of course, funding for the commission would come from taxing the rich or by cutting funding from school programs. Months would go by as democrats and republicans feverishly debated the funding of this much needed commission. Eventually, funding would finally be granted to fight these "obamanations". Of course, Texas would quickly be overrun, as their laws protect all life past the fetus stage, up-to and including the "feed-us" stage. After many years, the zombies would reach Colorado and assimilate with the like-minded individuals who would like to do nothing else but sit around and eat all day. All in all, it would be interesting none the less.
If we're talking Resident Evil zombies, then we add more criteria. If we're talking Shaun of the Dead zombies... Then I'm on the wrong side.
So, Resident Evil style zombies. Then, it depends on the virus itself. How long does it take for the virus to kill? And how long does it take for reanimation after it does kill? How is the virus introduced into the environment? A completely unexpected side effect of a cure for cancer, or a planned work of an evil billionaire genius, who has an underground complex, and automated sentry guns guarding every exit, shooting anything that moves, until it stops moving?
Depending on the answers to those questions, either everyone who had cancer becomes fast, strong, and brainthirsty (of course, Big Pharma wouldn't allow this scenario in the first place), or all the zombies die because the 200 automated sentries along the only exit... Each having a near endless supply of rounds....... While, all told, there are only 50 living things in the complex.
50/50... Try not to panic... Yeah...
That is what makes a takeover, if they were real that is, probably in that situation. You know the way there are various diseases that spread like wildfire and kill thousands because the population being affected has no cure? That is the same scenario we would find ourselves in, only this situation is a lot more gruesome than the Great Plague.
Most movie zombies are what I call "magic" zombies. There exists no way for any disease to infect a human body, and make it behave like it has rabies, but make it be able to move indefinitely with the lower torso removed. The circulatory system would fail and the body stop due to a lack of energy. A magic plague that can keep a dead boy animated even under extreme conditions would be unstoppable, and that is what a zombie plague is. Even most of the "realistic" zombie stories aren't based in the constraints of reality so there is nothing to worry about. For example, after 6 months even siphoning gas wouldn't work because it would have turned to sludge, but zombie movies routinely show this as working even years after the apocalypse.
So I don't think they'd do too well in a world filled with not-so-retarded people. Of course it depends on the movie, in some zombies aren't retarded, while the classic zombie is nothing more than a shambling annoyance. I guess if you went with the "Viral Zombie" you'd have problems since finding patient zero and subsequently a cure would be very hard the longer the response took and that is defined by how long the virus incubates; if it's for years there's no way.
The problem with the zombie invasions in movies is that nobody has any idea what the zombies are. Since you're suggesting a real-life attack based on those movies then we humans would have seen the zombie movies and would know how to counterattack.
If we assume they start in one location on Earth, it will be quickly isolated and quarantined. Military sent in to deal with the zombies will know zombie weaknesses and proper tactics for defeating them.
Really, we'd take note of the mistakes made in the zombie movies and design our strategy to avoid repeating them.
That means that when they eat your meat you dont have any muscle to get back up and move around. But lets assume you can get up and move around. Zombies are slower than us dumber than us and they dont have guns so there is no way they could take over the way they do in the movies.