Having said that, I do agree that really, you would need mass infection throughout the population, then the zombie stage later, in order for this to get really out of hand. Especially if people reanimate automatically on death, and it wasn't known at first. Hospitals might be the first places to get overrun, actually.
I agree. Something with a very, very long incubation period and easy transmission person-to-person could be endemic to the population before anyone even knew it existed. That would create the numbers needed to give the zombie plague a shot.
Going the other way - to 28 Days Later
, where any slight scratch turns you into one of the "ragers" in mere seconds - used to sound good to me, but it's got its own problems. One advantage to a slow-acting bug is that you can get infected and then drive yourself to another time zone before you zombie out - so the infection can effectively appear everywhere at once. The "rage virus" can only advance as fast as a man can walk/run after getting infected - and not even that fast if the victims don't move in straight lines. So if the "rage virus" appeared in California today, we'd have weeks
to plan how to stop it on at the Mississippi.