Ok, with the zombie invasion stuff up, people are already avoiding cities as it is. However, one thing I doubt many people know is that you can use ALL portals in shattrath as a zombie. That's right, an orc can teleport to stormwind if he's a zombie.
This being said, one can get a raid group of people to attack Ironforge for example, and have an infector turn all the raid into zombies, and then teleport to ironforge. From there, you can make a mad dash to the throne room and corpse explode to infect the elite guards and cause chaos. Then just corpse run and rez to have a cleared open room, clear of both the opposite faction and guards, and get a quick kill on whoever you need.
I have tested the portal, and it does work. I haven't actually tried a raid on the enemy yet, so I don't knoew how well that would run.
Bandefaca
EDIT: Picture of Magni downed
Code:
http://img516.imageshack.us/img516/5669/wowscrnshot102507223942ba1.jpg