Thanks for all the input so far. A lot of good stuff. I was a bit surprised by the initial batch of responses since it didn't seem like things had changed much in terms of what people liked since I read those books a long time ago. But I'm glad to see input from the single-layer, modern fiber folks to provide some perspective, too.

I was just curious because in my day hikes, I just wear one pair of synthetic socks and I've never particularly felt the need for two layers, but I thought that maybe that's because I'm not really going that far. But it sounds like even serious folks go with one layer, too.