Originally posted by Faceplant8:

I would love to see proof of any differences. I've done tests in the past and have seen absolutely no difference in anything.

Phase 1:
Make a new world, with whatever seed you would like.
Explore it for an hour or two, noting the locations, varieties, and counts of trees, mobs, etc.
Enter a burial chamber, note the layout.
Take note of the locations of metal deposits.
Take note of berry bush locations and numbers.
Take screenshots.

Wait a real-world week.

Phase 2:
Make a new world, using the same seed as the world created earlier.
Wander around, looking for the landmarks you noted during exploration of the previous world. Notice that the world created earlier is not entirely identical to the new world.

Tada! Proof that world-gen is only semi-deterministic.