I commuted with racks all last winter, 15 miles one way, I never felt they were unstable. I did have a messenger bag, and always feel that raises the center of gravity with the extra weight I'm carrying. On the bladder/water/ice problem. I never had a problem with the bladder freezing, there's usually enough insolation plus some heat from my back. What freezes is the water in the bite valve, and the tube. I have an insulation sleeve now, but still have to remember to blow back so the valve doesn't freeze. One other thing. I've got a friend who throws his bladder in his messenger bag, says it works quite well. I haven't tried it, but I did have a bag that hung fromt eh top tube that I stuffed a bladder in, was pretty handy, but the bag acted more as a sail than anything.

I've been collecting winter gear all year. I got a pair of REI winter gloves for $5 during the summer, set of studded tires when I was up in Grand Marais. Anyway, I live a mile from where the Luce Line starts in Plymouth. Maybe I'll see some of you crazy folk this winter. :D

As for hydration, I'm gonna try my camelbak under my jacket. We'll see how that goes. I'm sure it'll be good at least down to 10F or so.