Java: 1.7.0_25 64bit
OS: Windows 7 64bit
Whn you create a nether portal, the particles that it usually emits are all concentrated on one axis on the north most portal blocks. The spread of the particles looks more normal as you get closer to spawn (0, 0, 0).
At 30 mil blocks each portal has 1 emittion point.
At 10 million blocks, it starts to split into 3 emittion points.
At 10 thousand blocks, it has no distinguishable emittion points.
I have attached a picture of each of these samples below.