I'm confused...why build rails in the nether?
For portals? What about all the scenery?!
I love to ride rails and see the scenery, but that's more of a luxury than a legitimate form of transportation. Nether portals are dozens of times faster if you're traveling long distances, and are much much much easier to build. :shrug:
But you can always build rails in the nether to reach the really distant gates, making travel so fast it feels like cheating.

Edit: Erm, dozens of times faster, eight times faster, whatever. :spotted owl: