Red Ferret reviewed Liquid Armor, a "nanotech" spray that you apply to your mobile device screen in order to prevent it from scratching. They found it very effective and easy to use:
All in all we were very surprised (really!) to find that the coating does seem to actually work. It’s hard to believe that a spray on coating can have that much effect, but unless we’re missing something, it does appear to protect the screen very well indeed under stress. It works with glass of course, so don’t expect the same results if you have a cheaper plastic screen, and it pays to remember that the spray needs to be re-applied every 3 to 6 months to maintain protection.
Overall, we’re going to give it a 5 out of 5. Easy to apply, effective, low impact on screen functionality and not too expensive. We’d like to hear from more real world experiences, but for now it’s a thumbs up recommendation from us.