My buddy VJ Fader (Wen Cui) and I got invited to push our mobile video projection cart around during the Coachella music festival.  The cart is about 10 feet tall and made out of PVC pipe bent into five-fold symmetry with spandex covering.  Four 20 watt fluorescent bulbs hang on the inside to light it.  The power is a small gas generator or a battery system.  People loved it… a great response… lots of people came up to it and touched it or hugged it.  We’d like to go back next year with a grant… and perhaps build four of these:

More here: http://www.flickr.com/photos/74206512@N00/tags/coachella2008/

And here: http://www.youtube.com/watch?v=_XsUfsWE4wA&feature=related

http://www.youtube.com/watch?v=E_fpaYmkzfo&feature=related

As a side note: I built a parabolic solar cooker out of a square meter of cardboard, some aluminum foil and two coat hangers… cooked a stew on it one day… got too hot to touch.