Paper gets wasted a lot in offices everywhere, with people printing out memos that are relevant for about 15 minutes only to have all 50 people who got them toss them in the old circular file right after reading them. While email is a great and easy way to save paper and send your impermanent info around to your coworkers, sometimes you just need to have something printed out.
Xerox is all about saving paper while still using paper, as they sell paper, so they've developed some paper that will erase itself after 24 hours, allowing it to be reused up to 50 times. The sheets are coated with a special chemical that causes the ink to fade when exposed to light, generally 16 to 24 hours after printing, but the erasing process can be sped up by passing the paper through the printer again. It's the perfect technology for memos and love notes that you don't really mean.