To answer the hijack, steering is best accomplished from a crouched, wide stance because it allows you apply the most leverage to your knees. Joubert documents this fairly extensively when discussing braquage in "Teach Yourself To Ski" and "Ski the New French Way" (with Vuarnet). The extent to whether this is still a useful movement is best discussed in other threads.
To answer the OP, VSP gave a good answer. The point of unweighting is simply to achieve a full or partial decrease in pressure on the skis. When skis have both little or no pressure and they are flat, it is simple to apply a twisting force to them (in the horizontal plane) to make them pivot into a new direction. Up unweighting is accomplished by aggressive extension (usually preceded by gentle flexion) to project the CM in an upward direction. Down unweighting is accomplished by an aggressive downward flexion (usually preceded by a gentle extension to provide room to flex). Whether this provides a full release of pressure or just a partial release, there is no question that it alleviates enough pressure to allow an easy redirection of the ski. That said, unweighting is solely about pressure. What you do after you unweight is a seperate discussion.
Up unweighting and down unweighting are very old-school terms. IMO it works best to consider them as specific maneuvers as described above (and to consider them as involving simultaneous leg action). LeMaster goes a bit further to categorize up unweighting as occuring when the CM rises and down unweighting to occur when the CM falls. Personally, I think this distinction isn't interesting because it doesn't help me when I am skiing. I don't tend to think things like "for this turn I want my CM to go up..."
In any event, when it comes to release, which minimally refers to how we let go of the old turn, there is clearly unweighting going on since no matter what you do, you will eliminate the pressure on any ski that was pressured as a result of the previous turn. That said, I tend to agree with the sentiment that unweighting is not the same thing as release. The point being, that the kinds of releases that we talk about with modern skiing are performed with different movements than the old up and down unweighting. While retraction may look similar to a down unweight due to the extreme flexion, in retraction, the legs are pulled up. The "unweight" is due to the slingshot effect that happens when we quit resisting the forces of the old turn. This is just one example, but modern releases also differ from classic unweighting in that the pressure release may be sequential rather than simultaneous. Whether there is unweighting going on and whether it is up or down, is irrellevant to me in the context of modern releases. All I care about is how to do the required movements.
As to what the OP's instructor was trying to convey, we can only guess. One of the issues with releases involving aggressive flexion is that at the point of release, your hips are going to be behind your boots. Some people confuse this with being in the back seat, and while it technically is, it is a non-issue as long as the skis are light while this is happening (which would be the case if the release were done correctly). The larger issue is what happens after that. If your release involves a flex, you are going to need to perform some form of recentering movement to ensure that you are able to move your hips forward relative to your feet as you enter the top of the new turn.
The other issue that can occur with flex to release is failure to let extension occur with the new outside leg. Again, this isn't a fundamental problem with the release, its a problem with execution.
The OP seems pretty fishy to me. Not only are the terms being used wrong (I'm not aware of unweighting being discussed as an element of carving in modern literature and IIRC even Joubert specifically points out that you don't have to unweight when discussing straight ski carving), but it isn't clear what the intended outcome is supposed to be. Student centered instruction would not involve throwing out a perfectly good release just because the student isn't executing it correctly (you'd just address the deficiencies). Nor does the rationale about "los[ing] all the energy you've built up in the turn" make sense either. If you have potential energy and you quit resisting the turn forces by releasing your skis in *any* fashion that energy will be converted to kinetic and you will be pulled into the new turn. Hopefully, there is some grave misunderstanding going on here between the OP and the instructor, because what is being represented is patent nonsense.
To the OP, I'd stick with the release you know and make it work, rather than starting from scratch. There is nothing wrong with using some extension as your instructor suggested, but it also has its own issues if you don't get it right. To wit, you need to be careful that you don't start using your inside leg to push, or project yourself into the new turn. That kind of a movement can be hard to control and it usually results in your balance ending up on the inside ski. If your lateral balance isn't automatic, you may have trouble with this.
There are lots of folks out there that talk about "projecting" and "extending" to move into the new turn. Some of the folks talking this way may be very good skiers. However, you have to understand that there is always going to be a fundamental disconnect between the movements as they actually are versus how they get described in plain English. This is what makes teaching and learning skiing so difficult. You need to get your CM to move diagonally across your skis and foward into the new turn so that you end up properly in balance on your new outside ski. However, this should be a very controlled movement (aided by the forces of the old turn). If you view terms like "projection" and "extension" to mean throwing your body around or pushing your body into position, then you might do well to consider some new words.
In PMTS, we focus on the feet. We flex the old stance leg to release the turn (which also transfers balance to the little to edge of the uphill ski). This allows the forces of the old turn to pull us into the new turn. Meanwhile, we tip the old stance foot from big toe edge to little toe edge. This also helps move us into the new turn and it results in engagement of our new edges. The movements of the feet trigger the right things to happen in the joints higher up the kinetic chain. The movements are very controlled. We don't extend, rather extension occurs naturally as our skis take a divergent path from our CM. Recentering is accomplished by "pulling the feet back." I've put this in quotes because it is a relative movement. Our feet don't go backwards relative to the snow, but they do relative to the hips. The key is that the hamstrings need to be recruited for this move. Dorsiflexion alone isn't sufficient.
Edited by geoffda - 12/31/09 at 9:32am
The reason that flex to release is used is because it works for everything. Releasing by actively extending the legs is avoided because it doesn't work for soft snow and bumps and because it can lead to lateral balance problems when improperly performed. Since fore-aft balance skills are a core component of expert skiing, PMTS simply teaches those skills from the get go. The fact that you need them for aggressive flexion releases is a positive, not a negative. This meant to answer your question on the PMTS perspective--not to suggest that this is the "right" way to ski.