"I've had trouble with my Sigg bottles. They started to leak and the outside coating started peeling off!"
I've not had any of these problems to date. After some time the nice shiny exterior gets scuffed up a bit. I've also picked up a couple of small dents. One tip - if you live in a northnern climate, don't leave them in the garage over the winter in a with water inside as it will expand and rip open the bottle. Ouch!
The liquids do warm up quicker in metal bottles but it has never been something that bothers me. Eventually plastic bottles will get to the same temperature.