I have. In fact, I've had a hand in burning a few. Usually at the closing campfire of one of my Boy Scout Troop's campouts or summer camp session. Of course, everyone is usually standing there in silence and saluting, but we're still burning the flag.
Ah,
Of course, that brings up another issue; legally defining "descration"...
Every court in the country would be tied up trying to define it. Is it defined by whether you're saluting when you burn the flag? What about flag-clothing? An American Flag shirt is ok, but what if it's across the bottom of jeans?