What would make you keep a business card?

The size, weight and shape of the card is as important as the information on it. If it's visually appealing, then I'd like to be able to pin it to a cork-board I have at home. If you expect people to keep it in their wallets or purses, then you have to make sure the dimensions fit properly. Having a witty phrase is a good idea but it'll be lost if the design/application is poor. The interactive element is a nice idea too but if you make it too simple, people may not hold on to the card if they can remember what to do!