I absolutely LOVE this jacket. I ordered the jacket in a size S and I am 5'8" and 130 lbs. with an athletic frame. It fit perfectly. In fact, there is enough room underneath that one could conceivably wear more than a regular t-shirt or long-sleeve shirt underneath. The fabric is really nice and the quality is fantastic. The way the jacket is tapered, it gives you a waist so you don't look boxy.
I use this jacket as a layer for skiing on really cold days under a North Face Insulated ski jacket, for running, and for the beach/cool evenings in San Diego. When I ski, I use a moisture-wicking layer (Long-sleeve Under Armour), the Trollveggen, and then my North Face jacket. I stay toasty all day.
This really is the nicest multi-purchase jacket I have been able to find, and I always do extensive research before I purchase something. I tried on quite a few jackets at REI, but was not 100% satisfied.
Backcountry.com is awesome! They have great staff to answer your questions and the shipping is very quick. LOVE Backcountry!