Well, I'm not gunna bother reading pages 2-12 on this one due to lack of time, so sorry about all the repeats.
I personally think piercings are killer. Get a chick with a nose ring (and literally a ring, none of that stud bull shit) a couple lips a few eye brows and more ears than i'm worth, that's a perfect ten.
Tats are different, however. If you can pull off tattoos, then go for it, but if not, then don't. Unfortunately the only way I can tell the difference is if you get a tat.
Now, personally, I'd like all of this stuff myself (so it's not just pain I want chicks to go through) however employers really aren't into it, so I can't.
I really don't think there are any good reasons why people like tattoos or piercings. I just like them, it's been like that forever. I remember the first time I saw a mohawk, I fell in love. Corse, at the time I thought it was a weird birth defect, so my wishes were a bit mislead.