I recently read a few articles from around the the Internet regarding the debate surrounding the use of /64 or /126 prefixes on P2P links.
Here is a response I left on another site:
“The idea of using /126′s is little more than scar tissue from our experience with IPv4. It is the application of old ideas to new technologies and the argument that the addresses are being wasted is irrelevant. “We’re never going to use this many addresses” is a saying that is uttered with full knowledge that we said something similar 30 years ago (and we were so horribly wrong). We are afraid that we lack the foresight to anticipate what IP will become and once again allow history to repeat itself.
I have contemplated the seemingly insane; a world where jars of oregano and bottle caps have IPv6 addresses. If I give an IPv6 address to every single item in my home, including separate IPv6 addresses for each sock in a pair I cannot begin to tax the address space available to me as an individual. Corporate considerations are equally unaffected.
Using anything other than /64′s for any link is going to do little more than add an additional complexity with no solid benefit. The conservation argument is inappropriate and I encourage anybody who wants to make it to return to the drawing board with a calculator and some imagination so they can re-learn the futility of trying to put pressure on the IPv6 address space.
We will have figured out a technology better than IP long before we begin to put pressure on the IPv6 address space. This is true even when the day comes that we need to extend the IPv6 address space to support the United Federation of Planets. 
Colin Weaver”
