My thoughts on ski wear:
3 indispensable layers are: merino wool base-layer, uninsulated technical hard-shell top and bottoms with venting options and good hood, midweight insulating vest (fleece, thin down, etc...). This is where you want to start.
When properly dressed you should feel a little cold on the first lift of the day and the first lift after lunch. Your body has not had a chance to warm up. Once you are warmed up you will feel neutral not cold and not sweaty.
Waterproofness for ski outerwear is kind of over rated. It is only relevant if if there is actual precipitation and the temperature is above about 28f. Breathability is nice to have. But, if you are are not over dressed and have proper vents its less of an issue.
0F at 2,000' with over cast skies is alot colder feeling than 0F at 10,000' with bluebird.
Like the others said, what feels good to you is going to be very personal based on your own body and local weather conditions. Even things like did you have enough breakfast or did you have an extra couple glasses of wine with dinner the night before may have a huge impact.
Insulated ski wear is really nice to have -- but only if it is very cold. Skiing in a T-shirt and parka is very nice option to have. Check out the quality, lots of insualted ski gear have cold spots.
If I start feeling cold after a few runs, a thin light layer is all I need to add most of the time. e.g. medium weight long underwear top or a minimal thickness polartec vest is a great layer to throw on.
Keep in mind stuff like gondola / tram vs. chair lift, it will make a difference.
The big risk is not getting too cold because you are under dressed, but rather its over heating. Think about how you will cool off if you get too hot.
A powder skirt is not really necessary for ski wear at all. If you fall alot what you really want is bib pants. If you fall alot in actual powder you want a 1 piece snow suit, not a powder skirt.
Edited by tromano - 10/1/11 at 1:29pm