I used the Polar Cyclone Buff this weekend on a ski trip and it worked great!  Kept me plenty warm in 30 to 40 degree weather.  Almost too warm.  This particular buff is rather long, so it bunches up a bit around the neck when not pulled up, but it doesn't inhibit mobility at all.
Today I used this Buff while riding my motorcycle in 30 to 50 degree weather, with winds gusting up to 20MPH.  I never felt any of that on my neck!  My neck stayed toasty warm the entire 4 hour ride.  The ability to pull the non-windproof portion into my helmet was very nice and helped to keep me that much warmer.  The non-windproof portion is very soft and pretty thin, but it did add just a little bulk to the inside of my helmet.  Not so much that it was uncomfortable, but it was noticeable when first putting my helmet on.
A quick word on the windproof portion.  It is basically the bottom half of the Buff.  The windproof portion wraps around about 4/5 of the bottom half.  The last 1/5 is a fleece material.  I was initially concerned that wind and cold would creep in at that area, but it never happened.  Once I had it on I couldn't detect any cold spots at all.
Overall I'm very pleased with this Buff.  I would highly recommend it, especially for motorcycle riders in cold climates!