In reply to TobyA: I don't see the point of them either. If it's raining then you need a hood, and if it's not raining then you wear a windshirt and save yourself some weight and money.
By Gore's own admission, Active Shell's durability is an issue, and so in my mind a £300 superlight jacket should only be used where the difference in performance between it and another fabric is critical to success.
Regarding windproofness of Active Shell: it is completely windproof, just like 'normal' Gore-Tex, as its air permeability is zero. It might feel less windproof because the fabric is thinner, meaning that the increased bellows effect and buffetting from the wind will increase convective heat flow.