I got this email from Backcountry the same time I was at an REI class on winter camping.
Two things from the REI presentation I noted for myself that aren't described here:
One is the REI person flat out stated it isn't necessary to go out and buy a ton of new gear. That's in contrast to Backcountry saying you'll want a four season tent. I think I'll try winter camping in my three season tent some time, hopefully soon (but how is it already February?). I definitely do need a new sleeping bag and will add a closed foam pad under my inflatable pad.
The other is water purification which Backcountry doesn't address at all. REI said some filters will fail entirely if they freeze once (the expanding ice damages the membrane) and that UV, tablets, or just boiling water is generally better. I'll need to get a real stove as I either use solid fuel (Esbit) or no stove at all in the summer.
REI also presented on using a pulk (gear sled). I don't think that will be as necessary for me, but I'll have to keep it on the consideration list. It probably makes more sense in bigger groups where one pulk can carry heavy gear and fuel for all with the burden shared. I've seen pulks in the Adirondacks.
I'm still a little uncertain about clothes. I'm fine when active, but I worry I'll freeze once I stop to set up camp.
ButterflyEffect, do you have experience or interest in winter camping?