Mine fell off once, I was driving down the road and it fell into my passengers lap. It went back on very easily, it simply slides over the back of the mirror stalk.

Yes, there is some bare metal on the rear view mirror, I was surprised the first time I saw it too. But it's invisible unless you look up and back at the mirror.

 

Mine slipped off over a year ago when I was cleaning my windshield. I clipped it back in place and it hasn't been a problem since.
Hi crusty ~ I have driven this car for 2 years and have never found any random pieces on the floor. Maybe you are picking them up on the bottom of your shoe j/k I have seen this problem with cars that have had aftermarket alarms or stereo systems put in. The installers can't seem to put things back together the way they were

 

This is a funny thread. On my '01 that same U shaped plastic piece spontaneously flew off and into my passenger's lap. At the time we were not sure where it came from. I later figured it out but had not noticed the exposed metal prior to replacing the piece and thought there was another piece missing. I check a new model at the dealer and determined that is how it is. I need to check the '02 to see if anything is different.

I also found a 3 inch long piece of heat shrink tubing in the car and didn't give it any thought until I found the same thing in another guys S2000. Strange.

 

I think the "U" softens up from the heat of the sun and loses it's hold. Clipping it from the bottom doesn't make sense (unless maybe on the other side of the world in Japan gravity works the opposite way?)

Stupid design, I've actually experienced this same thing with my TL but don't remember metal sticking out.

Makes me want to get out paint and change the color of the exposed metal to black (cheap cast metal with the parting line and sprue breakoff showing!).

Maybe next time a VW owner tries stealing my antenna, I'll look to see if he's got nice rear view mirror trim to pay back the favor!!!