In reply to Fraser:
If you're after something extremely warm, but not too worried about palm durability (belaying etc) then I bought some Hestra Primaloft liner mitts. They weigh virtually nothing as they don't have any extra bells and whistles on the outside, but are ridiculously warm (600g Primaloft on the back of hand!!! 400g on the palm). Once I was scrambling up a steep gully in pretty cold conditions, bare handed as it was kinda loose and sketchy. I topped out with completely numb hands. I popped these on and a few swings of the arms later the blood was flowing.
The only downside is they aren't the most dexterous, but with mitts it is pretty much always a warmth for dexterity trade-off. They're my backup mitts I carry for friends/emergencies etc because you just forget you have them on you! Also if you want to get shells for them later Hestra do those too, and I think Outdoor Research still do the Mt Baker shells.
I got mine from the Ray Mears shop:
http://www.raymears.com/Bushcraft_Product/696-Hestra-Primaloft-Extreme-Mitt...