The 5s: Once, on carpet from about table height. No damage.
The 5: Three times. One on carpet, no damage. One from the hood of my car onto pavement while taking off in a hurry.
This happened. :/ The display still worked, and so did the touch screen in places where there was still glass. But I really like my fingertips and wanted to keep them, so I replaced it under AppleCare+.
Then sadly, I dropped the replacement about a month before the 5s announcement. That dinged a corner, but no broken glass or anything else. Still working well as a hand-me-down.
Previous models: Lost count, but maybe I had between 2 to three drops per iPhone model. Usually no damange, or just resulted in a scratch or minor ding.