Rating: 5 / 5
Update 3/15/2012: I found a great deal on this jacket and took the plunge once again, this time for keeps, and have also revised my score from a 4 to 5.
Why the change of heart? Well, a lot can change in a year. First off, the main reasoning for my score of a 4 earlier was due to concerns surrounding the durability of the quantum GL fabric, but I feel much better about the fabric now than I did a year ago - I spent last fall backpacking season and winter around town with a Rab Xenon, which is a synthetic fill jacket using the same GL fabric, and it has held up remarkably well. I've also been much more active in the past year and lost enough weight to the point that my size large Montbell is just too big. I decided to replace the Montbell with two down pieces, a sub 7oz ultralight down pullover for the majority of my 3-season backpacking, and the Rab for pushing 3 season as far as I'm willing to go.
I purchased this jacket as a potential keeper out of a group of three - the others being Westcomb's Kokanee Hoody (sadly way overpriced) and Montbell's Alpine Light Down Parka. The Rab and the Westcomb both use Pertex's new 10D weight Quantum fabric. It's extremely thin fabric, and combined with the suberb down used in the Infinity, it almost feels like it could pop (more on that later). The fabric has a softer hand than the 30D fabric used by the Montbell (but really, I feel the Montbell fabric has a great feel for the weight). Fit seems true to size.
As I mentioned earlier, the down used in this jacket is impressive, very lofty, easily loftier than the other 2 jackets and, dare I say it, probably surpasses the down in my WM Ultralite bag. This is a very warm jacket, warmer than the Montbell and Westcomb in my experience.
Regarding fill distribution, there seemed to be slightly less fill in the arms compared to the hood and the torso in my jacket (but this could just be me compressing the down in the arms with motion). The hood is just plain awesome IMO - despite it being non adjustable, it has great form fit to the head and moves very well. It was not designed to be helmet compatible (of no consequence to me, but may apply to others), but Rab did not skimp here on the fill, very warm and looks hilarious for your friends (I was told I looked like an earless teddy bear).
There were a few letdowns that ultimately led to my returning it in favor of the Montbell - the fabric was just too thin for me, I did not feel it would hold up to the test of time. It was also rather pricey - even after I found it on sale for $210 (Compared to the on sale price of $130 for the Montbell). Another was the zipper, the starter for it is opposite compared to typical US zippers (kinda hard to describe, just know it's a pain to get used to). My jacket also sprouted from the stitching a surprising amount of down during the few weeks I had it in my possession.
This jacket has a number of features I loved but ultimately my concerns over long term durability led me in a different direction. If Rab ever remakes this thing (same quality down, similar or slightly less fill weight) with a more durable fabric and more functional baffling, I'll be first in line.
Last word: Everyone should copy that hood, it's very functional, warm, and extremely satisfying.