In reply to TobyA: I also have one, and wore it a lot when still living in Scotland, both for climbing a skiing. But its like a buffolo top, which as Toby says, you wear all day opening & closing the vents as necessary. I don't think it'd be a good belay jacket as
-its a smock, not a jacket & thus not so easy to put on/take off
- designed to close fitting
- very voluminous in a sac
As for above comments on not being waterproof, its designed to keep you warm & comfortable but you have to accept that you'll be a bit damp in heavy rain (bit like a wetsuit won't keep you dry but you'll be warm)