The rabble rousers at the World Wildlife Fund (they re-named fake wrestling!) have created a new, PDF-type file format called WWF. It's a file format that CANNOT be printed out. The idea: save as WWF, save a tree.
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WWF is currently only savable and readable on Mac, but a Windows version should be coming soon. [SaveAsWWF via core77]
Here's a video telling us about all the trees we kill with PDF (but more seriously, a non-print file is admittedly an interesting idea):