I recently contributed an article about nipple piercing to a great website called the-clitoris.com. Previously I'd let them post information I'd written about female genital piercings. You can find the nipple piercing article here, and for convenience it is reprinted below:
The contrast of metal jewelry through the flesh of a nipple is truly exotic and striking. Nipple piercing defines the region, frames the tissue, and makes the nipple stand at attention (though it doesn’t necessarily cause the nipple to remain erect at all times). Prior to the early 1990s, when navel piercings became popular, nipples were the most prevalent location for body piercings. Modern piercing enthusiasts—particularly in the gay and SM subcultures—explored the erotic potential of their bodies and started what has become the current style of nipple piercing. These days, people from all walks of life are experiencing the delights of this piercing. For some, it is simply an aesthetic preference or fashion statement; for others it reigns as a favorite in the realm of sexual and sensual pleasures.
Female Nipple Piercing with Barbell, and Tattooed Areola
Nipple Piercing: Placement and Choice of Jewelry