I've had the stainless Zojirushi for a few weeks and have had the opportunity to use the mug a few times. The first time was with hot coffee and creamer. I filled the mug at 8am and was steaming hot at noon. With some coffee remaining in the mug, I tossed it in my car. When I got home at 6pm- amazingly the coffee was still steaming hot. Very impressive. 
The next morning I filled the mug with ice and cold water. At lunchtime I opened my mug and all the ice had melted, the water was definitely not ice cold. By mid-afternoon- the water had become room temperature. 
All in all, it's great for keeping things hot but not cold. It is advertised for both.