I get to see mine every day - one of the reasons I choose the iPhone is the form factor - thinness, size, weight. I want a phone I can slip into my pocket and not notice.
For this reason I have never, ever put my iPhones into a case. The closest I've come was a Zagg skin on the back of my 4S since the glass back was too slick for my liking.
Sure, it gets dinged up over the course of a year of use, but I'm not carrying around the Mona Lisa in my pocket, it's a cell phone, a tool that is critical to my day to day business and lifestyle, but it's not a museum piece. A few scratches don't ruin it for me.
Think of a few dings as 'character' and enjoy the phone in it's "natural" state