The mittens are an interesting idea. With gloves that actually keep my hands warm I can't use the fingers for shit. For gloves that I can use the fingers they're thin as all hell and my hands freeze.
Got to go with Burton on these. I've had other gloves like DC...which were crap in wet snow. I soak them every season in scotchbrite to let them last another season. I also use Shoegoo on gloves to give them more life. I swear by them, I would't ride anything else in cold weather. When it's spring I wear a DC park glove if my hands get too warm.