Recently I actually paid attention to the little signs I've seen in every hotel room I've been in for the past fifteen years...
Save the Planet!
Everyday millions of gallons of water are wasted washing towels that have only been used once...
blah blah blah the world will end probably next week because you are a bad person wasting water and precious resources drying yourself off with a clean towel.
The problem with this is water does not get permanently contaminated with Tide or some other detergent when it goes down the drain. Water gets recycled either naturally or through man-made treatment facilities, and besides that, detergent degrades and does not attach itself to water at the molecular level.
What re-using your towel in a hotel actually does is save the hotel company money, and that's fine, I get it, I'm a Capitalist so corporate savings are a good thing. Corporate dishonesty is not.
Corporate dishonesty that preys on the goodwill of naive people by using the guilt trip that we are destroying the planet with our personal hygiene is not only not a good thing, it's kind of evil in a manipulative sort of way.
At home, we re-use our towels, mostly because we are frugal and are trying to save the amount of time spent doing laundry - neither have anything to do with saving the planet. When I am on the road I will not re-use my towels because I don't like being lied to and, well, it's a nice break from routine.
Sorry to all you Green-types out there who are outraged at my hatred for my home planet...you're being duped and you really need to sharpen your critical thinking skills.