The 55xx/56xx Xeon's used on these boards have another limitation with memory: if you use 1.35v RDIMMs you can only populate 2 of the three banks per CPU (6 sticks per CPU instead of all 9). I learned this limitation the hard way on my SuperMicro dual-Xeon workstation build (forgot to RTFM...oops). If you plan to populate all three banks make sure you are using 1.5v RDIMMs.Just with this remember that the 5500/ 5600 series Xeons are going to be very sensitive to the number of DIMMs populated per channel. Not a huge deal for most applications but if you fill the DIMM slots with 1066MHz quad rank memory you end up running at 800MHz DDR3 max on the 5500 series as an example. In many cases more memory is going to be better than faster but it does depend on what you are running.
Todd, who did you buy from? I had the 3-4 day process time on my first one also. I ordered that one from pnieman. Also when I was at UnixSurplus/ MrRackables I got the impression that the CPUs/ memory were pulled from the units also so they would need to be configured.