You're absolutely right, I can tell whether a laser cut part is present though ~forever seems to be 'a couple of months'. Eventually the smell fades. I'm particularly sensitive to fire smell (we all are but I have my reasons for being a bit more paranoid than most) so this was a real problem initially for me.

To remedy you can oversize the part a bit and then sand off the burned edge, you can lacquer or paint it to stop the carbonized wood from escaping (though adherence of lacquer and paint is poor on the burned edge) and you can (lightly) sandblast the pieces.

Edit: I've added this to the article in the 'wood' section.