Yep, the fundamentals, that's what Klaus Mair emphasized in his SofaSkiDVD, and no surprise many of the more experienced instructors who worked with me as well. Stuff like initiating the turns early, skiing over the feet, and mmckimson's favorite: "Turn your legs!" are not only advice I remember, but something I hear every weekend at clinic!
Having only 1.5 seasons on skis (I was a slowboarder before), I was fortunate enough to start from the ground up inside a ski school and is an instructor myself, that and the ability to spend an entire weekend (including Fridays) skiing without leaving the mountain is a huge boon to my progress. The lifts open at 8:30, and don't close until 10pm. On a given weekend, clinic happens in the morning, then teaching, another clinic in the afternoon, for both Saturdays and Sundays, I don't think there was a day skiing when I didn't have at least one clinic! 
Asides from the half-dozen L3 instructors at my ski school, I've also gotten a chance to ski for a few days with Bart Barczynski from Whistler, not only is he an incredibly smooth skier, but an excellent instructor as well, some words of wisdom (from him):
(referring to turn initiation) "Here's a question: which do you want to last longer, the beginning, or the end?" ..."Nobody wants a slow, painful divorce eh?"
"The ski is an instrument designed to be put on edge, many people think they are windshield wipers and treat it as such."
I digress, as far as putting those theories to practice on the snow, I'm being watched more often than not, which translates into bad habits nipped in the bud before they become REALLY BAD HABITS. As for the instruction media, studying expert advice before I start doing stuff helped a great deal in the sense that it progress my skiing much more efficiently than just getting frustrated and not knowing what I did wrong. How does that work?
Before watching that Klaus Mair video, during my first season of skiing, I could not angulate to save my life, doubt setted in, I thought to myself, 'is it because I'm not athletic enough?' 'is it because I haven't enough experience skiing?' This kind of attitude would only lead to worse skiing. After watching Mair's video and pondering, the internal doubts were replaced with corrective advice, so when stuff isn't working I thought to myself now, 'angulation isn't happening, try lifting that inside leg, put more force forward, extend the outside leg, fight the banking.' In this regard, the theoretical knowledge drawn from the books/media made a huge impact on my skiing, even in practice.
... While carving GS turns (without poles), I'm now able to reach inward and grab the inside turn with both of my hands in the snow, to which my students would often try to imitate (and slide out)... I guess I'm helping them out by getting better myself!
1.5 seasons isn't a lot compared to the 30+ years of expertise from the senior instructors at my ski school, but I do feel that the amount of time and effort I've given in the 08/09 season does warrant a step up in the form of running gates... and it starts with studying the fundamentals during the off-season! More books!
