of who is going to be using the finished product. My dd is deathly allergic to walnuts, including the shells, even from casual contact. I cannot buy ready made items (from individuals or from shops that sell pincushions w/ walnut inside) that can't be machine washed or do swaps because I won't take the chance the creator used pins that had been in a walnut shell filled pincushion. To be honest, this trend scares the crap out of me. When my dd is older and on her own, I hope she remembers things like this that people wouldn't even think twice about, even knowing about her allergy.
Also I've read that walnut shells dull needles because they're like wood.