I saw these posts about DOMS and lactic acid yesterday and was planning to post but see that you guys have beat me to the punch on my main point.
After years of sore muscles after skiing - seemingly no matter what I did during the off-season - I started trying to read more about this, and the whole DOMS thing is very interesting.
As mentioned above, it does involve micro-tears in the muscle fiber. The pain we experience the next day that lasts for several days or up to a week, is a result of the swelling associated with these tears. (If you've overdone it on the slopes, no hot tub for you! Ice those quads after skiing! - And don't forget the vitamin "I" :D). Lactic acid does cause the burn we feel while skiing, but it is quickly gone out of your muscles within a couple of hours and is not responsible for the soreness that sets in later on. (Here is where our off-season aerobic conditioning - especially interval training - can help. It reduces lactic acid buildup.)
Anyway . . . apparently, skiing uses "eccentric" (as opposed to concentric) muscle contractions. During this type of contraction, the muscle fibers are actually getting longer even while trying to get shorter. There are not many sports that involve as much eccentric muscle contraction as skiing (horseback riding and downhill walking are two others), which is why it's so true when people say - the best exercise for skiing is skiing.
That said, some of the exercises you see in ski training programs can really help. And they tend to be the exercises that use jumping motions - like jump lunges, and jumping side to side over a line on the floor, and jumping on and off a step, etc.
But here's the thing - it's not the explosion upward that is the important part of the exercise. It's the
landing. Landing over and over again and catching your weight with your leg muscles. THAT is what will help the most. And that kind of excercise has gone along way toward minimizing DOMS during the ski season for me.
I say "minimize", because even with these exercises, I still get sore sometimes.
I also walk up and down stairs (again - walking down is the important part), or go on hikes that require me to walk down steep slopes.
But there is no doubt - skiing truly is the best exercise for skiing!
Involves using a step without risers, making an already hard exercise even harder. GREAT glute workout. 
All I know is that if I miss this cool down and stretching, I definitely feel the difference versus when I've done it - especially after skiing.
