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 the 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.
According to Wikipedia, "Oleophobic (from the Greek (oleo) "oil") refers to the physical property of a molecule that is repelled from oil. The most common lipophobic/oleophobic substance is water."
Fingerprints on iPhone screens have been a source of consumer complaints since the release of the first iPhone in 2007. This new feature probably doesn't prevent fingerprints, but it likely makes the grease easier to wipe off. (If easier cleaning doesn't satisfy your need for neatness, try Phone Fingers--pictured below--but you only have yourself to blame if no one loves you while you wear them.)