If you stand on a chunk border with high FOV settings (higher than normal, becomes more notable the higher you get, most at Quake Pro) and look in a certain direction (between -45 and 45 when looking south) you can see that the chunk that you are not looking at and wouldn't see if your FOV was set on normal is black. I suspect that this is caused by the Performance increases made in snapshot 14w30a, and that because of the changes made things that are considered out of the players FOV just wont get rendered, so that's the reason why it apears black.

I found it really hard to reproduce the bug, I only managed to do so once, but I'll explain how I did it:

1. Find a large underground room (seems to work best there, don't ask me why), I found the bug in one of these naturally generated (Minecraft-)perfectly round caves.
2. Find a chunk border with F3
3. Face south and slowly turn the camera, if you manage to do it right (again, I also didn't figure out how to do it reliably) you'll see what I mean.

I'll also include some pictures, so you can see yourself.
Also, this happened with Fast settings, 2 chunks render distance and smooth lightiing off, but when I changed to Fancy, 32 chunks and SL on it didn't change a thing.