Here are my layers (besides undies), from inside out:

Top:
Wear:
-Base layer top as hiking shirt (Patagucci Capilene 2 zip-T) 5.0 oz.
Carry:
-Patagucci Merino 1 crew neck (mid-layer when hiking in cold) 4.0 oz.
-Lightweight wind shirt 2.4 oz.
-Down jacket--Montbell Ex-Light 5.6 oz (for rest stops/in camp)
-Rain jacket, or hardshell if you prefer that term 4.5 oz.

Bottom:
Wear:
-Lightweight nylon pants 7.0 oz.
Carry:
-Capilene 2 base layer bottoms 5.1 oz. (in camp only)
-Rain pants/hardshell 3.1 oz.

Additional items for warmth: polypro fleece balaclava, Smartwool liner gloves, rain mitts, Goose Feet down booties (aaahh, cuddly warmth at night!) for sleeping. In cold weather, I take a Smartwool headband (while hiking to keep ears warm and in camp to supplement the balaclava) and an additional pair of lightweight fleece mittens.

Wearing all the above at once is sufficient to keep me cozy warm down to at least 15*F. If I know it's going to be colder, I can take a heavier base layer (Capilene 4) and a 100-weight fleece vest. If the cold spell happens unexpectedly, I will spend more camp time in my sleeping bag. If it's going to be quite warm and dry weather, I leave the mid-layer at home and take a fleece cap instead of the balaclava.

The layer that I wear the most is the wind shirt. It's great when I stop and it's just a little cool or breezy. I originally bought it to keep biting flies off during rest stops, and it's great for that, too. For hiking actively uphill, the wind shirt over my hiking shirt/base layer top works fine into the low 20's F. Going downhill, I need the mid-layer if it's in the 30's F or below. The wind shirt also blocks wind coming through the stitching on the down jacket, making the latter a lot warmer. If I don't take the mid-layer and the baselayer top I wear for hiking gets grubby, I can put the wind shirt over it for sleeping to keep the dirt from getting into my sleeping bag. The wind shirt is the one layer I would never leave at home! I use it around home a lot, too.

I've looked with some longing at Goose Feet down pants. I prefer using a baselayer, though, because if it's below freezing, I wear the rain jacket and pants (non-breathable) as a vapor barrier. For that, you want a lightweight base layer under the vapor barrier. Like Brian, I change into the baselayer bottoms after I get my tent set up (normally the first thing I do when I am ready to camp). The other problem, for me, is that my rain pants aren't big enough to get on over puffy pants without seriously compressing the insulation. While I'd rather not go into too much detail about my dimensions, I will admit that I have quite wide hips!

With our mild winters where I live, the above setup works out fine for me during winter hikes, too. That means I don't need a separate set of clothing in winter, a considerable savings. Of course if I lived in Wyoming, that would be a different story! I'd have a much warmer down jacket better suited for -20 to -30 F temperatures, for starters.

As is obvious, I like using layers to fine-tune my body temperature. If you don't feel the need of that, fine. I wouldn't ever leave my wind shirt home, though--I wear it more often than any other layer!

This again, is a YMMV (Your Mileage May Vary) sort of decision--experiment and see what works for you. It helps that I can experiment with such things while exercise-walking around home when we get those howling east winds out of the Columbia River Gorge every winter. The temp may be about 25-30*F, but the wind-chill factor is more like zero F.