I have seen an other post about this but it is ancient and i think i need to add some information to this issue.
Zombies attacks are easily avoided. Maybe its a bit to soon to bring this up since there is still many issues with the Zombie AI but whenever you have a zombie after you.. just run in circles (using A and D and the mouse to rotate) and he wont be able to hit you. A circle with 2-3 meters of radius will do the trick.
This may seem like a small issue but i don't think so. It influence the whole game play. If zombies are no threat no cooperation is needed between players to defend or survive against them.
Being able to avoid some of the zombie strikes by strafing is something.. but being able to avoid 100% of its strikes, avoid 100% of 2 or 3 zombies attacks/punches at the same time by only running in circlea is a bit far-fetched.