I just got back from 4 days of using my Marmot Lithium (same fabric as the Versalite) in constant sub-freezing temps and was going to post a similar topic. It appears as if most people agree that the condensation around the face opening is from your exhalation trhoughout the night. I noticed this both over the past 4 days in my Lithium, and two weeks ago in my Helium. Though I did not breath into the bag/fabric, there was either ice or alot of moisture on the bag around the face opening.
But, like Ryan, I considered this to be a problem. Whether ice or drops, I could not just stuff the bag without attempting to remove the moisture as it would all be forced into the insulation. Gentle removal (shaking, wiping) would get the large drops off, but there was clearly some wetting out underneath.
By the 3rd day, due to this, the loft around the face of the Lithium had decreased and the bag felt damp there. Given that this was due to exhalation, VBLs would not likely help much.
Temperatures never got above freezing, and the sun never really came out, so it was not possible to dry the bag. Also, not every trip (climbing) allows for the time needed to do so. This also occurred last winter in my Helium bag. I dont think it is always possible to dry out a bag in the winter or on every trip, and the moisture does eventually get into the down in select areas and will make the area damp and deflated (in my experience). This does tend to take a few days, but it keeps happening to me.
Note- if the sun is out, the bag will usually dry adequately in a few hours, but that is not always a possibility.
I was going to ask what people do in these situtaions. I am thinking of either using a bivy, or a bag with a more water-resistant shell fabric. However, every bivy I have used gets frosty (Equinox ultralight being the one I have used the most), and both options add 5-7 ounces. If such weight additions are necessarry, a light synthetic bag (SD Volt maybe) that could be used as a clothes dryer (perhaps supplemnted with a hooded down jacket) may be a better option (cheaper, more utility, no VBL needed).
Given that ones exhalation in sub-freezing temps can in fact cause loft issues around the face of the bag, and drying out is not always possible, what does everyone suggest?
NOte: I wish other makers offered "Drishell inner panels at head to protect against breath soaking the down". That may be the lightest solution.