I play the iPad and iPod version of the the World At War zombies and I have noticed some useful / game ruining glitches.
iPod Version Glitches:
1) Shi No Numa has a glitch to where if you open up the stairs and camp next to the window closest to the bouncing bettys, all the zombies will spawn and attack that one window.
2) If you have running zombies, pause the application and re-open it and continue your game and they will be walking very slow (useful in high rounds)
iPad Version Glitches:
1) If you have running zombies, exit the application and re-open the application and continue your game - the zombies will be walking very slow.
2) Online functionality doesn't work on the HD version.