In my local club, the rule is you FOLLOW the rules of the road. We tend to go through stop signs/lights in as compact of a group as possibe, but not everybody can always make it though. In this case, those that go through should "soft pedal" until the rest of the group gets through and has a chance to catch up.
Regarding passing - people do it quite a bit - sometimes you want a different view, you get a burst of energy, though they should warn that they are "on your left" or "coming through".
I'm not a great downhiller either, I do my best to stay to the right so I can be passed. If I have the opportunity at the top, I suggest others get in front of me then so they don't have to pass later. This has the added benefit of giving me experienced downhillers in front of me whose line I can follow to help me improve this skill.
"Bicycling is a big part of the future. It has to be. There's something wrong with a society that drives a car to workout in a gym." -- Bill Nye