Would you be so kind as to explain what MacWhatsit is? And why his/her interpretation is so highly regarded that it's up all over the internet?

Also, does he/she give any insight into exactly what, and where, this Arci/Arcy is/was? (Normandy is big, y'know!)

I'm not doubting you, or him/her, you understand. It's just that this explanation is so often trotted out as a reason to explain Darcy's rank, that I'd really like to know if it is actually possible.