Merrells, along with the thinness of the upper. My hands tend to be cold when I run in cold weather, but not my feet. I do wear wool socks to help keep in warmth in case my feet get wet, since the upper extends very close to the ground and there can be some water seeping in if the road is wet or slushy. So far I've run in 4 degree weather where my legs felt very cold, but my feet were perfectly warm.
The basic concept behind this is that your foot muscles are in use so much more than when they're being supported by arch support and all kinds of padding that you're pumping blood through there much faster. I don't really have anything to compare with, since I've never run in conventional shoes in wintertime, but I have been hiking in winter boots and had my feet feel extremely cold/numb. I know my feet are much more muscular than they were before I started running, so it seems to make sense that that's why they're not cold (muscles in use generate heat, right?), but I don't have any specific information on it. Anyway, just thought I'd share that experience, in case there's people out there wondering how that goes.
Meantime, my Merrell Dash Gloves have over 1000 miles on them and I'm hoping to try out Skoras soon, since Merrell seems to have converted their entire "Barefoot" line to something less minimalist than I'd like to see. I'll post a review once I've used them for a while.