Ah lame, running zombies are impossible.
Not so. It worked pretty well in the "Dawn of the Dead" movie remake from a couple of years ago.
The latest developer interview stated that the replayability factor of the game is going to be pretty high due to the fact that zombie spawning is not fixed in the game. I guess each new game resets how the zombies are populated and you never know when or where they'll pop up. Sounds like a cool feature.
However, it seems each multiplayer co-op session will be short (play through to survive in less than an hour), but hopefully the offline campaign is longer (not much has been said about that yet).