Well, I had high hopes to commute all winter this year. But I lasted maybe one month into the "cold morning temps". When it finally got consistantly lower than 20F for my morning commute (done at 4:30am), I couldn't keep my feet and hands warm enough. Only 5 miles, but uphill and I couldn't feel my feet. I did get to ride some in Dec 06 when our temps were mild. As far as heat, I melt when it gets too hot, but I have finished a ride when it had reached 100F. I can't get enough liquids in me at those temps. I sweat profusely....