Recently bought these to protect my mitts during cold evening winter runs.  I was a little worried because they looked to be simply knit (and are) and I was worried they wouldn't keep my hands warm, especially in wind.  Some decent reviews though so I thought I'd give them a try.  I've since worn them on multiple snowy, cold winter runs with the thermometer dipping down into the 20s - these things have been fantastic.  My hands stay warm, but *because* they're knit they ventilate and my hands don't sweat.  They also fit extremely well and are very snug, which is a great feeling (like a soft, 2nd insulating skin).

If the cuffs were just a tad longer I'd be even happier, but my jacket is long enough in the sleeves that it fits over these snugly and with elastic keeps out all wind.  I will say that you *do* feel the wind through these if it gets particularly windy/cold, but again for me my hands still don't get cold.  You'll notice it mostly when first walking outside when it's very cold and breezy, but once you're running and start generating some heat?  They're just about perfect.