The number 12 is one of the coolest numbers in existance.

There are 12 thoracic vertebre in the spinal column, 12 beers in a half-rack, 12 disciples in an entourage, 12 signs of the zodiac, 12 months in a year.
There are 12 inches to a foot, 12 hours to a clock, 2 x 12 hours to a day, 12 x 5 seconds to a minute, 12 x 5 minutes to an hour, 12 x 30 degrees to a circle, 12 months in a year, the sou can be divided into twelve deniers and there are 12 dozen in a gross.

Why is the number 12 so prevalent in our lives? Why is the number 12 so prevalent in our systems of measurement? Well, the number 12 is unusually divisible; the numbers 1, 2, 3, 4, and 6 all divide evenly into it. By contrast, the number 10, on which our number system is based, can only be factored into 2 x 10.

The base 12 multiplication table has more simple patterns than the familiar base 10 multiplication table. For example, every multiple of 3 ends in 3, 6, 9, or . So do all the multiples of 9. Multiples of 4 all end in 4, 8, or , and so do the multiples of 8. Multiples of 6 end in or 6.

There are many, many theoretical advantages to base 12 notation; and there are groups of people that are dedicated to the notion of promoting "dozenal" (or duodecimal) notation... most notably, the Dozenal Society of America, and Dozenal Society of Great Britain.

^{ Sources for this writeup include:
http://www.studyworksonline.com/
http://www.dsgb.orbix.co.uk/ and mebreathing, whose post was tragically destroyed. Any other notable occurances of the number 12 that you know about? /msg me!
}