I've had a problem with frozen thumbs at below-freezing temps. I wear Saucony running gloves as liners under ski mittens, and usually my hands are fine. But, we've been having windy 0 degree nights (I ride home from work at 11pm), and by the time I make it home (6 miles) my thumbs are painfully cold.

To solve this wind issue, I cut a hole in the bottom corner of a couple 1 gallon plastic ziplock bags and slipped them over my handlebars. The bar ends on the mountain bike help keep the baggies in the right position since I have those bar ends that make an almost 90 degree angle out in front of the brakes.

Essentially, this is a poor mans poggie and REALLY cuts down on wind chill on your hands! I'll take a few pictures when I get home tonight.