Here's a neat idea - create an object you can wear (in this case Carbon Goggles) that when worn, show you the real world carbon emission data of the object you are looking at (if it has emmissions). For example, if you are wearing the goggles while car shopiing in SL, you will see the emissions data of the car!
This is very much under development. See this YouTube video for a taste.
Also, http://carbongoggles.org/ for the main site.
What a great idea! I'd love to see a real-world counterpart!