I bought this as more of a casual around town piece of clothing, living in Denver CO. Typical uses for me include going to a Rockies game, running errands in the morning, or hanging at my sons lacrosse practice in early evenings.
For these purposes i love this vest, it's so light you barely know it's on, so you have full range of flexibility, yet for as thin as it is, it's remarkably warm. I'm actually planning on using under my soft shell at Loveland in a few days, and i'm expecting it work wonders. Oh yeah, and did i mention it looks good, I actually received a complement at a bar about it.
Fitting is spot on, i'm 6'5', 230 lbs and bought and XL and it fits perfect, not too light but not baggy.
My only negative is that i do find feathers popping through more than I thought I would.