Usually it doesn't matter which of the slots you put the memory in. I say usually because some boards, such as my Abit BH6 were fussy early in their release cycle. There don't tend to be any performance issues (such as memory running faster in one slot compared to another) re which slot the memory resides in, rather it tends to be an issue of stability or downright running.
The max # of slots on the backplane of a case is 7, and w/ the placement of the CNR/AMR slots utilization isn't an issue. It's much the sames as the PCI/ISA usage issue - one or the other. That and there don't seem to be any CNR/AMR peripherals available today. They'll end up being more for system integrators that are always trying to save a penny here and ther.