Noticing that //regen will not be possible on the main world anymore due to biome changes. Additionally I'm seeing some weather pattern changes in some locations, particularly extreme hills with a certain height.
EDIT: Weather changes for extreme hills, particularly snow above Y95, is due to 1.7.x, and not a world problem. Nevertheless, 1.7.x has changed other weather patterns too (eg. taiga biomes no longer snow unless they're cold taigas), so bear that in mind.
Combined with existing //regen problems in 1.6.4 (including spawning a broken village - it's to the west of my tower area), I'm beginning to fear the possiblity of world corruption.