MacDailyNews discovered that Apple has introduced something new on the iPhone 3GS's screen specs: an oleophobic coating on the screen. Oleophobic, according to Merriam-Webster, means "having or relating to a lack of strong affinity for oils."
According to Apple's Cleaning iPhone page:
To clean iPhone, unplug all cables and turn off iPhone (press and hold the Sleep/ Wake button, then slide the onscreen slider). Then use a soft, slightly damp, lint-free cloth. Avoid getting moisture in openings. Don’t use window cleaners, household cleaners, aerosol sprays, solvents, alcohol, ammonia, or abrasives to clean iPhone. If your iPhone has an oleophobic coating on the screen (iPhone 3G S only), simply wipe your iPhone’s screen with a soft, lint-free cloth to remove oil left by your hands and face.
Keep in mind products like iKlenz and others that address the oil and fingerprint problem. Oleophobic material will never fully prevent the smudge, so these are affordable products to invest in to restore your iPhones original shine. :)
Why not just invest in a screen protector? So if you have to wipe the screen to clean it, you don’t run the risk of scratching it.