As part of the 2008 World Expo, interactive floor designer Sensacell has built a 250 square foot installation from 1000 of their LED panels. Covered in strong, architectural glass, the floor responds to pressure by lighting up. And while that alone doesn't sound all that exciting, the system tracks the pressure over time, allowing users to create a transient series of footprints that, I dunno, looks all the Sahara in the year 2832 when man has used all the sand to make those bottled sculptures you see at the mall. Check out the clip:

The purpose, of course, is to remind the public of our ecological footprint (but instruct us to keep buying those floors that so necessarily light up!).