I'm with Oregon Mouse on this one, though I (fortunately) don't have the experience of sleeping in either type of completely wet bag. I live in Washington state and hike a bit in the rain, and I definitely prefer a down bag ... it's just significantly lighter and packs smaller, and I've had no problem keeping it dry. I hiked the PCT this past year, and for the entire trip (2600+ miles over about 5 months) I used a down bag; I believe the majority (perhaps the vast majority) of long distance hikers use down bags or comforters. It's just a matter of taking the sort of reasonable precautions that OregonMouse mentioned.
Brian Lewis