Just a quick note on how setting up the boots properly has a huge impact on the skiing of each and every one of us. Here's an example of the difference a simple boot cuff adjustment can make.
The boot cuffs are supposed to follow the shape of the tibia and most race boots allow it to be easily adjusted. In this instance, the boot cuffs were left at factory settings (middle of the range) and the skier has a hard time balancing on one foot.
They do not always have such a huge impact, it tends to be more subtle, the but little imbalances resulting from improper alignment and setup can impair an expert skier - the more advanced the skiing, the more precise the equipment needs to be setup.