Interesting backstory here.
Edit: Listening to Zep's version this morning in the car on the way to work, I remembered one of the most amazing musical moments I've experienced.
A decade and a half ago, we were all camping somewhere out west (Great Sand Dunes, probably) and in the evening Phil brought out his acoustic guitar and started noodling around. Then he started playing this beneath the stars, and with each note, the campground got quieter and quieter until all you could hear was his playing --and the crickets. It was an amazing shared moment.