A few days back I created MC-29307 which described how the same seed may give some differences between users. But it was closed because the mods kumasasa and mustek could not replicate the issue. Now, I've found a way to replicate it

1. Create a MC world with a random seed (1.6.2 and modless)
2. Go far from spawn. ie 500 blocks
3. Shut down Minecraft, restart the launcher and load the world again (not sure if this is necessary, but it's what I did)
4. Go further from spawn and look for a jungle (these seem to have most differences)
5. Create some screens and note the coördinates.
6. Do the same on a different PC, different account, of course also 1.6.2 and modless
7. Create screens of the same coordinates. Differences will be visible.

I did it first three times on my own PC only, the locations in the jungle were the same each time, proving the plant growth is not rando.
Afterwards, I did this with two friends of mine, and they had some different versions.
We did extensive research and also found some differences in emerald ore placement in caves! (I'll place two new screenshots of that one) This is rare and me and my friend walked quite a bit through the caves to find such a spot.