I was born an amblin' man, and the Mammut Ambler down jacket is the way I do it. We're talking a Schoeller Nanosphere dirt-repellent soft shell plus 750-fill down insulation at about 3lb total weight.
As usual, Mammut nails the details. Two large inner mesh pockets accomodate quart bottles, an external zipper chest pocket holds small items ready to hand, velcro cuffs keep the draft out and the isulated hood fits comfortably over a helmet.
This jacket shines on belay duty, with a zipper that goes both ways (like... oh, never mind!) and a rear hem cut long to cover your ass. I used it exclusively as my ice climbing belay jacket this spring, and my partner sucks so I stood around a lot in it. It's plenty warm by itself to -10F, and with good base layers could go farther.
Mammut and Schoeller are both Swiss companies, so in the European fashion the zipper is off-handed for Americans. That's honestly the closest I can come to a fault. This jacket is as perfect as gear gets.