In reply to neuromancer:
> He says a lot, but he never really comes down on either side, or offers recommendations for different activities.
He does say a lot, and I've not had time to read it all tonight, but the reason he doesn't give a definitive answer is because, as with all things 'it depends'...
The one thing I'd suggest adding to a 'conventional' layering system is a pure wind resistant shell, which I wear unless it's actually raining. It's more breathable than a waterproof shell, but continues to provide the protection for the insulation, which, as AK points out, it next to useless for holding on to warm air in the presence of wind; that's the downside of a fabric (fleece) that is open structured to maximize trapped air volume in a light fabric that also allows sweat to escape from the body.
There are many advantages of separate wind resistant shell over fixed (e.g. pile/pertex); versatility in layering (selection prior to use, selection during use), ability to replace individual layers, ability to care for individual layers.