I think belly button piercings are hot because you don't know they are there until you actually get physical with the girl & then you are like, "Wow!" I just think it's sexier than any of the other piercings that you can see. I think it would totally turn me on during sex if my girl suddenly got one and we were making out and I found it - especially if I know she did it just to turn me on! I don't think I'd be as turned on with the nipple piercings though. I'm also not really turned on by having a girl's "private" area pierced. I just think that would be kind of weird. Those are just my thoughts anyway! :)
Pierced girls look very hot generally! I appreciate there are a miriad of sheep that say "it looks so trashy", but piercings are a fantastic stamement of individuality. They are also fantastic to play with!