Might want to do a preliminary restart when we get the Bukkit RB, just to make sure the NPCS are able to breed.
Newly generated villages should be okay, I think.
Anyways, since Naru had reported that zombies could break doors on normal (and there was a mention about it on the wiki), I did some testing and found that even with a horde (and I mean HORDE) of zombies attacking the door, they can't break it on normal. Meanwhile, I checked how it is on hard and it breaks the door there.
I believe they added the door breaking graphic in 1.3 when zombies are banging on it, so it simply looks like they're about to break through. I didn't see them successfully breaking down a door in a village yesterday, so I'm pretty sure that they actually can't on normal mode and it's just the new door breaking graphic.