Hannes Kalk has created a very interesting interface using non-newtonian fluids actuated by speaker motion.  I had considered this form of interfacing some time ago, but had dismissed it as being too messy to maintain as a consumer device, and difficult to consistently control.  Nonetheless this is a new interface that has some similarities to the issues that I am myself exploring – from the Creative Applications Network:

Imagine surfaces start to communicate with you. Your mobile gets goose skin when your lover texts you. Your WiFi controller changes the look and feel of it’s surface according to different game situations. Your sofa gives you a short massage as a warm welcome when you return home from a hard day of work. Your laptop feels dried out when battery status is getting low.