My iPhone 4 seems to be just as scratch resistant or more than previous models. Not one scratch yet and it's had a couple.. incidents where I thought for sure it would have been.
The iPhone 4 is definitely not as scratch resistant as previous models.
I even retract my previous snarky, "You're holding it wrong" statement.
Here's my story:
I got my iPhone 4 on release date (actually, the day before). I've had no issues with scratching it till today. My aunt came over to check it out yesterday (Saturday) because she wanted to see it before buying one, but she was worried about not having a screen protector like she's had on her HTC Touch Diamond. I told her not to worry, since it's glass, not plastic, and I've owned every iPhone since its release without a screen protector and it's been just fine. I ran my basically non-existent fingernails over the screen to show her what I meant.
Now I've done this test with EVERY iPhone - the 2G, 3G, and 3GS. I EXPECTED the iPhone 4 to fare the same. But no! I made three or four long thin scratches down the screen, and I'm not especially happy about it. I can feel them with my nail. So, whether it's the oleophobic coating or the glass itself that got hurt, something gave...
So there, if you think the iPhone 4 is as scratch resistant as previous models, I can tell you it's certainly not.