Here are two very good YouTube videos of Ed Ward, the Jedi master of Skagit casting, demonstrating and explaining the art. This is a must watch for those who are interested in Skagit casting as it is very enlightening. It covers the history and development of Skagit casting briefly and goes on to demonstrate the finer points of Skagit casting and how it differs from other form of Spey casting.
In this video Ed talks about water tension being the friend of a Skagit caster and stressed on getting lots of line on the water (full contact) and waiting for the line motion to stop before moving on the next stage of the cast. While this is true for floating Skagit head, my experience with intermediate sink Skagit head (Wulff Ambush Clear Head & SA Skagit Extreme Intermediate) however tells me that water tension can sometimes become too "friendly". Intermediate sink head can sit too low if left too long in the water column and in this case, full and prolong water contact becomes a hindrance. Once the water surface developed too much grip on the fly line, energy will be sapped from the cast when sweeping to form the D-Loop and the cast will not go well. Cast that performs well for intermediate Skagit head are those that the line only sit on the water surface briefly. For that reason, I often turn to the Speed Poke when using intermediate line.