Hi David, without wishing to hijack the thread entirely (it's related, at least, since Ventile garments are favoured by the "bushcraft" community who prefer natural fibres in sympathetic colours) I can say that I love the smock and have been using it for over five years. I opted for a front map pocket and Velcro cuffs (to allow more ventilation to my arms if needed). The hood is wired and excellent in a storm, the shirt itself is superbly breathable and windproof.
The key to single-layer Ventile is to wear the right thing under it. I generally use either a Paramo shirt, an Ulfrotte wool top or a Marmot baselayer, all of which help to control both sweat and the inevitable intrusion of water. Eventually, given enough rain, the smock begins to leak, but it takes a long time and I've happily worn it through Scottish downpours that have continued for days. A friend of mine wears a double-layer Ventile jacket and stays entirely dry, although he can't wear it in blazing sun as I can with the smock.
No coatings to peel, no chemicals to re-apply every few weeks, it's quiet and tough... and a very soft green so as not to stand out too much. Expensive, but worth it.
EDIT: Missed your question about the weight... On my digital kitchen scale it reads 654 grammes, which is a hair over 23 ounces, for a size Large. Since it replaces a windshirt and a waterproof jacket I can live with that. Indeed, when hiking I pretty much live in it.