Thanks for starting this thread, Tim:

As Tim suggests, the number 12 is significant in many areas of science and humanity. We even have 12 units on a standard clock face, which must be taken directly from old sundials...

I'm guessing that 12 is employed in so many things simply because it is a much more divisible unit than the number 10 is. (10 cannot be divided exactly in thirds... 3.33333, etc) But there are no doubt other hidden reasons why we use 12.

This link is a good intro to the daisy wheel layout of prominent medieval buildings:

http://www.cressingtemple.org.uk/Adrian%20Gibson/Wheat%20Barn.htm

No doubt Ken (and Gabel) can add to this...