I'm sorry if this has already been address or discussed. I just got my Due and have not been following the forums. I was trying to understand the SPI on the due and noticed some things. There is no indication on the board of the orientation of the 2x3 SPI header. I could only find the answer by looking at the pinout post here or testing for the power pins. There should be some indication on the website and/or silkscreen of pin 1. Then I noticed the ICSP header and was confused as to the difference until looking at schematic and seeing it is only for the U4. Maybe I'm unaware that the SAM cannot be ICSPed then? Either way its header was labeled as "SPI" on the silkscreen but on the SPI page http://arduino.cc/en/Reference/SPI
in the connections table it shows the pins labeled as ICSP-x for the Due. I could see people connecting SPI devices to the U4.
Also, and this is probably answered somewhere else (forgive me please) but why is the SPI header and the two connections by pin 22 5V when nothing on the board can handle 5V? Is this for mega shields?