I recently purchased a pair of Mountain Hardwear WindStopper Tech Pants and had occasion to use them over the Thanksgiving holiday. With a pair of lightweight Capilene bottoms as the first layer I found them to be quite warm and absolutely windproof. The temps were in the low teens at night and "warmed" to the mid twenties during the day. Wind was brisk about 10 knots. We spent the weekend in the Olympic mountains of Washington State. The fleece portion does collect snow, however, the nylon seat and knees shed it quite effectively.
Bottom line: I'm very satisfied with the product, in fact I'm very satisfied with all my Mountain Hardwear clothes and gear.