I've ridden in rain and wind and snow and had my windshield completely ice up on me in the Smokeys this past February. Going over a chunk of ice can be a VERY harrowing experience, definitely not something to play around with. The other thing besides the Gore-Tex or waterproof gear is to make sure your boots have good non-slip or grippy soles. My boots tend to wear out in the soles (my other 'emergency brakes') and those have led to quite a bit of a dance trying to hold up my other bike on slippery ground.

As for trying to make sure everything stays dry... scoot more than a couple hours in torrential rain and it really won't matter what you've got on, water will always find a way. I usually have to make sure my gloves go over my sleeves fully (I have gauntlets) and that I wear my water-resistant wind gaiter over my jacket instead of under as usual.