Photo courtesy of granitegeek.org
Another blogger has written a good and extensive post about this, take a look here. Most of the comments are great too. But some missed the whole point of his article.
The main point is - do not leave your windshield wipers sticking straight up. You will wear out the springs and getting the blades stuck to the windshield is not really a big deal. Damaging the blades also isn't a big deal, you can replace them, but the blade springs are much harder to replace.