tl;dr: The first time I've put a case on my iPhone—and kept it on after a week!
I have always disliked iPhone cases. I've owned every iPhone since the beginning, and have never used a case; instead of a case, I kept the phone in a holster case on my left hip.
Every once in a while, I tried a new case, but returned it to the store within a day or two. There were always too many tradeoffs in terms of usability with docks and different headphone and dock plugs, and most cases made the phone harder to hold and use.