The feel of the furnace blowing warm air out the vent right at the end of the bed as it wafts up under the blankets......
They have their place. It sure makes relaxing after a day on the water nice. Amazing what a little hot water, a furnace and a queen size bed will do for you.
That being said i would still jump at the chance to take one on a back country trip. In the lower 48 there just are not too many places left where it is required, more the shame.
I still have my old 3 man from my single days tucked away in the attic.