Derek, the issue is moisture from your lungs causing mildew inside the mat, or degrading the down in the down-insulated models. Also, when it's cold out and you inflate your pad with warm lung air, it will contract quite a bit as it cools. Start with cold air from a pump-bag and the problems is mostly avoided.
RE: your PM... I use mine on top of a Tyvek groundsheet and sometimes a thin blue foam pad. As usual, site selection is important, but I haven't had to use the patch kit yet. Can't imagine durability is any worse than other inflatables. Enjoy the PCT!