I love this idea! I hate using a bar of soap in showers that isn't mine- those little hairs that get stuck on it, the confusion as to whether or not a bar of soap is clean since it's soap. (Disclosure: I very rarely, if ever, use a bar of soap that belongs to someone else).
But what a great idea this is! It's like a cheese grater for soap! By Nathalie Stampfli.