In reply to iksander:
Speaking as a long time (and I mean a l-o-n-g time) dead fingers sufferer, who's tried everything from £1 handwarmers to £200 battery operated gloves, in my experience the gel handwarmers are pretty poor. Though they get quite hot quite quickly the heat lasts only minutes. For the rest of the day your then carrying the dead weight of hard, heavy, useless lumps - come to think of it that sounds like one or two of the seconds I've had over the years - no offence boys!
I now manage the best I can with at least one spare pair of really good gloves kept warm about my person, as opposed to in rucsack, and disposable handwarmers which, whilst not getting VERY hot, at least stay warm for many hours and don't hinder ice tool handling too much. Whilst belaying I retain the handwarmers and change into the warm gloves.
If you're not familiar with them it might be worth mentioning that the disposables sometimes have a job "starting" if it's REALLY cold. In these circumstances it's probably best to "start" them before you leave the house/hut/car then when you come to need them they'll be nice and cosy. You hope. Maybe you can buy less plastic bottled stuff to offset your handwarmer pollution?
Good luck.