They dont matter to me. I encourage them in fact. If I do find it too distracting after the fact, its gone with a minute or two of photoshop. I sometimes have them take them out but not all the time. I never make a model remove a new piercing, id rather edit it out instead.

I have 4 holes in my ears, my nose, lip and navel pierced and they haven't affected me.  I often have to take them out but you can't see any holes in the photo's and the photographer's apparently haven't had to photoshop them out.  I very much doubt a few ear piercigs and a navel piercing are going to affect you. 
Just remember that you may be a model but you still have to be happy with yourself.  If modelling makes you happiest and you think the piercings will be a problem then take them out, if you really like the piercings then leave them in.  The modelling world is so diverse, if you were constantly changing yourself to fit in with someone else's ideal you'd be a mess.  Everyone has there own idea of beauty and what's right and wrong you can't possibly please everyone but you will always have to live with yourself.

I shoot a fair amount of work for cosmetics companies in Europe. All, without exception, state that models must not have tattoos or piercings other than one piercing in each ear. I have also been given the same instruction from several fashion houses.

personally I think when tattoos are done PROPERLY then can be beautiful but I've seen a lot more that look like busted ass. Its a risk anyone who gets a tattoo has to be willing to take. But if you're a model and your body is your meal ticket, why take the chance? And as far as piercing it can be and asset or a hindrance. depends on who you're working with and what type of modeling you plan on doing. But again, why take the chance?

And there is NOTHING John Casablanca's can teach you that you can't learn for free.