Kevin Eric Snell

Hard to say. I never had this problem before 1.6.1, can't say what caused it, and haven't had recurrences since 1.6.2. The only world-affecting changes you'd see from a mod would be in the lighting of watery areas (I turned on Clear Water in OptiFine) and some Redstone problems from using X-ray. To my knowledge, the corrupted chunk had no Redstone circuits, but it did have Water, so who knows.

Not sure if you use MCEdit or not, but if you do, try doing what this guy did http://www.minecraftforum.net/topic/1746628-exception-in-world-tick-crash/

Meh. A little OptiFine, a little X-ray here and there, and that invalidates the whole thing? You're meanie-heads. BTW, I fixed the problem following this advice: http://www.minecraftforum.net/topic/1746628-exception-in-world-tick-crash/ It required dinking with MCEdit, but hey, live by the mod, die by the mod, I guess.

I can cope with untidy villages. The only real problem is houses that suddenly go up/down one level halfway through, so the ceilings and floors don't match up.

Suggestion: villagers should be programmed with a kind of "wanderlust," if there are too many villagers in their immediate vicinity, that prompts them to wander in a random direction for a while, checking occasionally to see if there are doors nearby. If they find themselves in a place with many doors and few other villagers, they'll get the urge to settle down in the new location.