"it's so light, does it really keep you warm?" YES!
This jacket is great. I wore it home for the holidays, and my friends and family were very skeptical when i told them to feel how light it is... but when they tried it on, they were amazed at how warm it is! Walking from my car to the stores when x-mas shopping, i was perfectly warm, and when i got inside, i didn't have to rip it off (like i usually have to with warm stuff, like my Patagonia R4) because it's very light and comfortable, and i could wear it inside without sweating. haven't tested it in the rough outdoors yet, but it keeps me toasty warm in my icebox (89 Volvo, which takes an eternity to warm up!)