I have developed my evade skill to some extent and it gives 6% more chance to evade. However, I have fought several battles and what I have noticed is, that I use this skill only in round 2 (I am a ranger and round two is the first round an unranged opponent can attack me).
In the evade skill description it is not mentioned if it works only once in a battle, through a certain period of rounds or each and every round (as I assumed first). I hope we will have detailed information about how the rest of the skills work on game mechanics too.