Adafruit is a great resource for may electronic projects. One of my favorite parts is their focus on wearable electronics. Gizmos with LEDs and speakers have been around for a while. You can even get them from Thinkgeek. However, capacitive touch with conductive fabric opens possibilities.
I’m not sure if this ever will become mainstream. But imagine having sensors for vitals integrated in your t-shirt. Monitoring pulse, breathing, etc without any clumsy sensors. This, coupled with movement-based power generation, I’m sure we will see more and more in the future.