I have my belly button pierced, and I have had it for about 7 years almost. I like mine.. I'm beginning to get sick of it but I still like enough that I won't take it out.
The jewlery that you wear in it is actually called a belly button ring, and can be a hoop or a barbell.. I have the barbell type.
As for the pain factor, it didn't hurt me too much. Kinda like getting stung by a yellowjacket.. but after that it was fine. And you can definitly change the jewlery.. I don't do it often but its easy if you want to do it.
As for pregancy though.. thats the one thing i'm afraid of, bc i've heard that the hole stretches out a lot when you get larger in the belly area.. not something i'm looking forward too. But oh well.. not much I can do abou tit now.