This 32 year old mother of 3 has one.
I love mine!
I got it for my 28th birthday... I was finally starting to get my old body back after having my 2nd child.
I had no problems with it... it was quite sore for about three days, but I followed all the instructions and it healed nicely within a year.
Then, I got pregnant again... I wore it up until the 9th month and then I slipped it back on the day I got home from the hospital.
It inspires me to keep doing my crunches, cardio, etc... and I like the way it looks. It's a personal thing... either you like it or you don't... but for me it is symbolic of a sort of peace I have made with my body.
I used to hate my body but instead I decided to give it jewelry. The navel ring is a symbol of my love and respect for the amazing body I have been given and the things it can do... I have great pictures of me with a HUGE pregnant belly and a litle gold ring sticking out!

And I have pictures of me with a flat stomach and the little gold ring shining.
It's a celebration of my belly after years of hating the poor thing.
edit: Tripleshot, yes, it is a generational thing. And Mr Isla had a FIT at first... but that may have been part of the reason I did it.

I got the idea from watching all the girls on mountain bikes... My family was a bit surprised, but in the end it is so personal and private, no one minds.