My fiancee has a Giant Rincon SE and uses it as an all-weather commuter/utility/long-distance bike.
During the past couple of winters, especially during heavy cold winds she's experienced problems with the drive-train. Sometimes the tension in the system goes out and she is able to freely pedal with no resistance from the chain. The problem is not a skipping chain. This happens for at least 5 seconds at a time, several times within a mile.
My amateur mechanic mind thinks the problem might be the freehub's rachet-arms are getting stuck/frozen in the sub-zero conditions, thus not moving the wheel when the cassette turns the freehub. Do your expert minds agree with this theory or could there me other causes?