I live in washington and face the same problems as you do. My commute is only 2.8 miles on the way there but the ammount of water kicked up at me sucks. I just orderd some shoe covers by hincapie and I have a waterproof jacket and pants that work wonders. I love my headskoz!!! If it weren't for that I probably wouldn't bike in the winter, it keeps your face nice and warm! As for keeping stuff in my bag dry I've used plastic bags on everything, can't be too careful. I've finally accepted that I love commuting and could care less what people think about my fun little habbit. I change in the bathroom, you don't need a shower after 4 miles of riding, if you are sweating profusly in this cold weather maybe you need to go a bit slower. I go at a slower pace in the morning but after school is out I go fast and take a longer route home for fun.