If 90 percent of the world population actually became infected like it seems happens in the movies ( or more). How long who'd it take to kill them all? Or before their bodies broke down so much that they did not matter anymore anyways.
Other questions: Zombies be effective in cold climates? Zombies bring many animals close to extinction or are they too slow?
I think the Zombie situation would last about as long as the Black Plague lasted. Aids was only really a problem for about 20 years. Zombies would become depressed or bipolar before they ever evolved into something better. Do zombies evolve?
That last question would be more for Jay520 to answer.