In reply to climber34neil:
I have one.
My experience has been that it's too warm for me if I'm active. In order for me to use it as a "put it on, leave it on" sort of piece, I'd have to be in really really cold conditions. I haven't used it as much as I thought I might, because it's too hot when I'm active, and not warm enough when I'm just standing around.
However, I run freakishly hot, so it might work better for other, more cold-blooded folks.