Intel allegedly has some problems with the amount of PCB layers needed for motherboards with its X58 chipset for the Nehalem processors. FUD Zilla says motherboards will need eight-layer PCBs to resolve issues with the three channel DDR3 memory design:
The issue is the trace length, as these have to be done exactly right when it comes to memory, or the timing of the data will be out of sync. The more PCB layers you have, the more space there is to put the traces down, and normally motherboard layouts start out at six or eight layers and are then reduced to four or six layers.
However, in this case it doesn't seem to be as easy as it has been in the past and Intel is even asking its motherboard partners for help. It might still be possible to reduce the PCB layers needed, but it will take time, although with some six months to go until the launch, there might just be enough time to resolve this issue.