I'd be interested to know if any of you who own an eVent jacket feel it necessary to also carry a windshirt. Having owned and used an ID Thru-Hiker jacket for a year now, I can say that the jacket has worked for any condition that my windshirt was good for (a Rab Quantum WS). And by ditching the windshirt, I save 3 oz, which justifies the extra weight of the eVent jacket (versus a windshirt plus lighter but less breathable jacket).
One of the things I like most is that, once I've got my jacket on for cold or wind, I'm all ready to go in case it rains. I have been known to just keep the jacket on all day whether it rains or not. This is a real convenience during intermittent showers.
I find that the combination of windshirt and eVent jacket is too warm in every condition I've tried it in, so I don't see an advantage with combining them. Plus, I use a Cocoon Pullover which, when added under the jacket, adds the equivalent of 2 windshirts. So if conditions are truly foul I've got the extra protective windbreak layers built into the Cocoon.
Yet, every major publication on UL hiking technique suggests the four layer approach which includes windshirt and jacket (though most of these were written before the lightest eVent jackets hit the market. Anyone care to come up with a list of pros and cons? This of course assumes the decision has been made not to use a poncho tarp.
The only downsides I can think of is that I will wear out and/or clog with oils my eVent jacket sooner than if I used a windshirt, and that a windshirt drapes better, so is a bit more comfortable for casual use. And okay, I suppose I look a little weird wearing a rain jacket for bug protection.

