Robustness and durability are typical qualities that we aim for when building interactive prototypes and systems. Tanja and Axel explored what user experience we can create when we deliberately design something in a way that is ephemeral (=not lasting, there is a good German word "vergänglich"). Ephemeral User Interfaces are user interface elements and technologies that are designed to be engaging but fragile . In the prototype that we showed at TEI 2010 in Cambridge the user can interact with soap bubbles to control a computer. Axel has some additional photos on his web page.
There is a short video of the installation on the technology review blog: http://www.technologyreview.com/blog/editors/24729
 Sylvester, A., Döring, T., and Schmidt, A. 2010. Liquids, smoke, and soap bubbles: reflections on materials for ephemeral user interfaces. In Proceedings of the Fourth international Conference on Tangible, Embedded, and Embodied interaction(Cambridge, Massachusetts, USA, January 24 - 27, 2010). TEI '10. ACM, New York, NY, 269-270. DOI= http://doi.acm.org/10.1145/1709886.1709941