I hate cases, and screen covers even more. The iPhone is so beautiful, I don't like to cover it up. That said, it's a slippery bugger. I only dropped my 3G twice, both no damage. For my 3GS I felt like I had better get a case. I've gone through four and ended up disliking them all except one. InCase Slider. I bought my wife one. She loved it. So, I got one, too. Excellent. Great, tactile feel (black, pink, the titanium and red are metallic feel) and hugs the phone so it still looks like an iPhone. So many are just bulk. It's been on a month. Still liking it.

As for screen protectors, forget them. The screen is very strong is very resistant t scratches. I've had three iPhones. In my my pocket with keys at times. Never a nick.