I have Invisible Shields on almost every small electronic product I own. My 2 iphones, my ipod, my macbook, my treo, and my DS. Aside from being a PITA to apply, they are the best things in the world.
I never worry about scratches, never worry about too many fingerprints, much less prone to fingerprints/greasy look than the plain iPhone.
They also DO NOT leave a sticky residue, ever.
No company has ever given me a problem with the warranty because of it.
Also, a lifetime warranty with no questions asked, they even send you the new one before they ask to send yours back. My Treo fell off my car when I was dumb enough to leave it on the roof while driving. The treo was fine with a few scratches on the shield, I told Zagg the story, I had a new shield in 3 days.
I recommend it to everyone I know who wants protection on any small device, much better looking than any cheap silicone case and doesnt take away from the aesthetics of the device.