I've used a bivy bag over the down bag, and most of the condensation ends up on the inside fabric of the bivy. It will eventually build up, though, just over a longer period. In real cold, use a vapour barrier. If you're a tiny bit clammy, that's okay, but if it gets really clammy, it's probably not cold enough for the VB. The other answer is to wear a couple of layers of wool inside the VB to avoid the clamminess. I never really minded the vapour barrier. If it was cold, I knew my bag would still work a week down the road. Irrelevant for the mountain man. He'd be in his cabin most nights, and the odd overnight would be in a tent with a woodstove. That 20 lb 5-Star bag is pretty dang comfy on a bed of spruce boughs in a canvas tent. Truth is, the down mummy's are warmer if you go expensive enough, but the comfort and durability of the 5-Star is what makes it great. Be nice if they put a bloody footbox in it, rather than a straight edge.