In my opinion, ANY extra protection I can put between me and bullets is beneficial. Even if you can maybe scavenge a helmet, so people can't cap you in the back of the head as easily? And yeah, I think it would still have to be very weak - the game is about teetering on the verge of death :P It would ruin it if it was possible to be invincible - the strategy would change from be smart to survive, to find ALL THE ARMOUR! to survive :P Just for examle, armor that made it harder for zombies to make you start bleeding, for example could work, and it could have little effect on bullet power.