Creative Die Cut Business Cards

We recently saw a clever die cut for a make up artist that specialises in teen 'how to apply make up' classes. The card featured a semi-circle cut out from the top of the card, with instructions that the card should be held against the eye before applying mascara, thereby preventing mascara from getting on the eyelid. This was not only a great tool for the make up artist to promote their business, but it was easy from a design perspective as well. How can you use die cuts to enhance your customers' business cards?