I took mine out when i fell pregnant i have a scar left and can still get the bar half way through the hole either side but not all the way through. My scar is a bit like a smiley face only small thats the best way to describe it
mine's been out for about 8 months - but its still open - when it does eventually close it'll be kinda like the little smiley that tigilou described - you can get some scar reduction 'pads' from boots - can't remember what they're called but I don't know if they'd be suitable for belly buttons.
On a happier note I removed mine and only have two barely noticeable dots! Massage the area regularly when you remove it, this helps reduce scar tissue.