When ordering prints online, you would think it be as easy as a 1-click solution.
Not so for users of iPhoto an Aperture it seems.
According to this article at Apple's Knowledge Base you really have to watch what aspect ratio the image was taken in, to avoid it from being cropped unexpectedly.
No one wants their wedding pictures returned with the head of the bride cut off.
http://support.apple.com/kb/HT2024