In reply to Appleby:
Only time I've experienced "Hot Aches" to any great extent was when snowball fighting at school, them days when there was snow on the ground the school used to lock us outside during play time so as not to trudge snow in and out of the corridors, (how times change) we had no gloves and I'm a shit shot, coming back into class was 10 minutes of hell!
Now I can usually anticipate them coming on and nip it in the bud by warming hands, on a bike you can always stop to warm up, when climbing here's what I try to now do.
1) Belay where possible your second in guide mode, gives you more freedom to warm hands.
2) When belaying leader stick on a pair of overmitts, as its rare you need the dexterity in this situation.
3) try to do everything with gloves on, once there on they should stay on. If you have to take them off then shove them inside your jacket next to your chest to keep them warm. Putting on a pair on gloves that's been lying in the snow is a recipe for worse than hot aches.
4) as others have said, if your cores get cold, your hands are the first to suffer, so keep it warm and FUELED!