Still too early...
I originally bought the Patagonia Stretch Element as my hard shell jacket for skiing and other activities. It is a great jacket in terms of quality and function but I've found the Patagonia to be a little too much of a snug-fit when layered with as any typical size mid-layer. I'm 5'9 and around 160 lbs. I wear a medium. When I found the Arcteryx Theta (Spring 08) on sale at Altrec, I decided to return the Patagonia and get the Arcteryx. The Arcteryx is just as good as the Patagonia in terms of quality and function. The fit is perfect with a mid-layer and the fit doesn't feel too baggy without one. So far, a great buy.

Great shell, crazy sizing
Great shell, well worth the extra cost. I just came back from a few days of spring skiing in Tahoe. The temps bounced all over the place (20-60) and I couldn't have been more comfortable the entire time. Everyone else was changing after just about every run. However, the sizing is a bit strange. I'm 6' 180 lbs with broad shoulders and the Medium fits reasonably well with room for layering; there are about 600 places to adjust the fit, so you can tighten things up as needed. For context, I wear a Large in the Arc'teryx soft shell and it fits perfectly.

Just what I would expect from Arc'Teryx
I am 5'11, 175 lbs with a 40" chest. I bought both a L and M to try on and ended up keeping the M. I plan on layering this shell with a light fleece all the way up to my First Ascent down sweater and the M fit perfectly around by body with the arms the perfect lenght. With only a T-shirt the M fits a little loose. The reason I went for the Theta is for its long coverage. The jacket fits like a suit at the sides and extends past my butt in the back. I have not gotten a chance to test the jacket yet, but the jacket is well made and the exterior material feels like it can take a beating. The zippers work smoothly with no binding and I really like how they are waterproofed thus eliminating the need for annoying storm flaps. The pit zips are nice and large with the same waterproof zippers used thoughout the jacket. Although pricey, I am certain the Arc'Teryx Theta AR jacket will last me many seasons and amortized, will pay for itself with use.

Perfect Spring Skiing Jacket
This jacket is as durable as any I have ever used. It comes in very handy for backcountry trips where wearing a pack and encountering branches, rocks, etc is commonplace. I have never had any water soak through. My only complaint is that it could have a chamois cloth for goggles, detachable powder skirt, as well as a Recco reflector built in.

Excellent Jacket
Superior construction when compared to other makes. I am 5'11'' and 165 lbs. The large fits great with room for layers. Breathes well and has pit zips for greater moisture and temperature control.