I don't like to draft on people when I can't see what's in front of them. It's one thing in a race, but if you are on a group ride with non-racers, sitting-in blind is an incredibly bad idea. I was on a long ride a while back and I kept warning the guys in front of me of hazards. I wouldn't normally do such a thing, but the first 17 swerves made me realize they weren't exactly thinking ahead. We were all pretty wiped out by that point