"Flawed Poll" because it doesn't include "It depends on the situation."
I already overheat easily on rides, so wearing lots of heavy armor is rough. Also, I have yet to find much protection that doesn't chafe my knees when pedaling. I don't wear gear while climbing if I can avoid it - I've gotten some nasty cuts and abrasions going uphill, but downhill involves so much more speed and momentum. Every climbing fall has been slow motion, and I can often catch them. On the descent, a lot of times I don't even perceive a moment between losing control and slamming into the ground. It feels instantaneous.
I always wear hard plastic elbow, shin + knee, and full face helmet when downhilling - I also have a neck brace, but I don't wear that much anymore because I'm not pushing myself the way I did a few years ago, so it feels silly (stupid reason not to wear it, though). I also had a full chest protector at one time, but now I wear the G-Form tee that has a little bit of padding on the shoulders and chest. I figure that my hydration pack will provide some protection if I fall on my back.
I've seen some nasty injuries on downhill, btw. One woman who grabbed the brakes after a little bit of air on an easy trail ... a guy who didn't wear a FF helmet on a black diamond trail at Trestle and broke his orbital socket ...
I always have G-Form elbow and shin pads with me on my rides (the knee pads don't work for me). They take almost no space in my pack. I rarely wear them, partly because I don't feel like taking off my shoes. But the other day, I rode my first real trail of the season. There's a descent that is just continuous jaw-chattering rock, from gravel to baby heads. I've ridden it many times and never been injured, but I had some jitters, so I wore the protection as a hedge. I think it gave me a little shot in the arm to allow me to ride fast enough that the rocks didn't totally mess me up.
On a related note, I wear men's baggies to ride. They seem to make a big difference when sliding on dirt and rock - I don't get the road rash that I'd get with bare skin or even spandex shorts. On me, they come down to just below the knee. I do not understand women's baggies, which are 1) not actually baggy and 2) expose most of the leg.
