I keep massaging mine and trying to break up the scar tissue! I read that's what you should do with c-section scars (once they are healed) so I figure it might help with this too!
I didn't take mine out til bout 25 weeks so it ended up with a massive nickel sized scar that's dark purpley with whitey/yellow streaks because it was rejecting. It's gross. =[ The actual holes are closed up though.
But its starting to fade. I've been putting a stretch mark belly butter on it a couple times a day that has vitamin e and cocoa butter. I know they say it might not help, but it seems to be! It's shrinking and I haven't got stretch marks on it yet, but we'll see I guess.
One of my friends got stretch marks from hers and a little dark sunken area (though they aren't bad really in my opinion!) and the other had none at all and was able to repierce it a few months later and it looks great!! I think its one of those things. =( Luck of the draw.