Quite fun indeed . Trap doors should be added to the mob griefing list .
Hmm, yeah, trapdoors, and any type of wood doors. I think i remember them not breaking ghostwood and other modpack wood doors. Have to test.
The other thing to add to the "Me not likey, Zombie Smash!!" list would be any of the microblocks made out of glowstone. I'll admit to using quite a bit of those around my base currently