Stain Teacup: Age is Beautiful? - Gizmodo:
The interior surface of the cup is treated so as to stain more in predetermined places. The more the cups are used, the more the pattern is revealed. Over time they will build up an individual pattern dependent on the users personal way of drinking tea.
In a culture that prizes the new, I'd love to see such principles applied to popular electronics. Instead of the constant fear of scratching your beloved iPod, the only user who could reveal intricate designs would be be long-term user.