I tried one of this things a few months ago and reckoned they'd only be good for supervisors and managers (i.e people who stand in the cold watching others work). They are kind of nifty but I doubt I could wear one for more than 5 minutes if I was actually working or doing anything physical.
I was looking at them, pretty good idea i think, but like Krafty said good for people who stand and watch. Would also be good on a winter camp i reckon!
I know the feeling, I used to wear shorts and short sleeves all year round when I was driving the truck, even working 10pm to 10am and through winter in areas where Satan skated to work each morning being fully covered and physical was just a waste of time. Working was more than enough heater even in temps below 5 degrees. However had they been around 20 years ago when I worked at the council supervising road crews I would have had 3 of the buggers.