Augh. Why can't I ever finish a thought?...
I've tested 4 different bags in the last 7 months,sleeping in the backyard. The ones that boast a DWR finish seem, at least so far, to deliver. Most recently, I slept in the Somnus 30, which has a Pertex Quantum shell, when I woke up in the morning there were little ice-balls all over my bag. Apparently I bumped the center pole of my tent and rained condensation down during the night. It beaded up and stayed there long enough to freeze. It definitely didn't soak into the shell.
FWIW: I'm not a particularly warm sleeper, and the Somnus 30 was cool comfortable in just polypro baselayers, wool socks, and microfleece beanie at 30*, or maybe 29. I had frozen condensation drips on my bag, ice in my Nalgene, and weatherunderground.com temp history to check.