For a recent trip to the snow, I picked up a Zippo brand catalytic hand warmer.
I tested it at home a few days prior, and worked fine. In the field, it worked, but took a little coaxing to get lit (windy conditions + Zippo lighter did not equal fail, but it meant more work.) I ended up putting a little bit of Ronsonol in the catalytic burner (bad idea, I know) to get the thing touched off. But once it started, I had warm hands in <10 minutes.
Compared to disposable hand warmers, I noted that the Zippo lasts about as long, but comes up to temperature much faster (seems to me the disposable ones can sometimes take an hour to reach full heat.) One lesson learned is to keep the warmer in an inner pocket (I had it in the shell of my parka) - it retains more heat that way, and in a chest shirt pocket you get the benefit of additional warmth for your core when not using it for your hands. The other lesson learned is to get it going a few minutes before you're out in the sticks, the wind and sub-optimal conditions for the use of flame.
Overall, for the $19 I paid at a local surplus store, I think it's well worth it and will get a couple more to keep in my camping and fishing gear. The only downside is that no matter how careful you are, you get a pretty good whiff of lighter fluid now and then. I'll pay that price for the convenience and reusable nature of the item.