Thanks for the great list, now it's far easier to create my Xmas wish list 
An idea came into my mind when reading this discussion. Could shield manufacturers place a mark which pins the shield uses? e.g. a square or a circle around the pinnumbers or just inverse print the number on the shield itself, or don't print the numbers used as these pins are not available? As I have no experience in designing boards I do not know what's possible or easy to do. Are there reasons not to mark the pins? e.g. some pins are optional and others aren't? Different markings?
Just thinking out loud,
Rob