When you do wash a down item, be sure to replenish the DWR finish on the outside afterwards. The Western Mountaineering website has excellent instructions for laundering down. As already mentioned, when you try to wash a down item, you'll find out how resistant it is to getting soaked.
Note that, despite some claims by the synthetic insulation industry, wet synthetic insulation is no warmer than wet down insulation. (Been there, done that.
) Regardless of the type of insulation, you must keep it dry.
In the pack: use dry bags (not stuff sacks) or tightly closed mylar (turkey roasting) bags or line your pack with a 2-mil plastic bag (trash compactor bag--be sure they're unscented) or contractor trash bag or other waterproof liner. Test the liner periodically and replace if needed. Check daily for small holes and use your duct tape. Pack covers will NOT keep your pack contents dry--heavy run runs down your back and into the pack, and if you slip and fall during a dicey stream ford (again, been there, done that
) it won't keep the water out of your pack.
On the trail--don't wear your insulating jacket while actively hiking; use a thinner mid layer instead (for me, a wind shirt and baselayer top, plus cap and gloves, are sufficient down into the teens F). The idea is not to get chilled, but to at all costs avoid sweating into your insulation. The insulating jacket is to keep you warm when you stop hiking. If it's raining, keep it under your rain jacket.
When camping in the rain, set up your shelter first (it should be accessible without having to expose your pack contents to the rain) when you stop, and take it down last when you break camp. Do all your unpacking and packing under the shelter.
Even here in the Pacific NW during the rainy season, we usually have a midday "sun break." Take advantage of these to air out your tent and sleeping bag. Even 15 minutes helps!
When it's below freezing, a vapor barrier inside your sleeping bag really helps keep the moisture from your body from condensing--and possibly freezing--on the inside of the outer shell of your sleeping bag. Just remember not to wear your insulating clothing inside the vapor barrier, because it will be damp inside. Wear only your base layer (which should be a fabric that doesn't absorb moisture) inside the base layer. Different folks have different reactions to vapor barriers. I do fine as long as the outside air temperature is below freezing. Others have to get into much colder temperatures before the air inside the vapor barrier ceases to become a sauna.
This new dry down stuff sounds interesting but (being a bit of a skeptic and not having much $ to spend at this point) I plan to wait a year or two to find out if it's helpful enough to be worth the extra $$$. It hasn't been around long enough to get widely used in Pacific NW winters, which IMHO are a pretty good test of moisture resistance! I hope that if anyone here tries it, they'll report back!