Go figure. I'll try that out next time I'm playing it on Post-Human Warrior mode.

http://www.youtube.com/watch?v=y0fBuZzaFY8&feature=player_embedded

You can run around meleeing enemies in PHW with or without that. Takes about half a second to kill somebody with melee.

There's a better version: Break the door of an ambulance. It works as a riot shield and seems to mess with the AI. If you face them while holding it, they literally cant see you / ignore you. When they shoot at you about 2/3rd of the bullets hit the door, rather than you. You can then melee them with the door for the win