Since the character growth in this game is going to be largly based off of weapon use, I think it'd be cool if your character's skill with a weapon was displayed by the way they weilded it. This is purely aesthetic.
For example, if someone just began to use a great sword their movements would certainly show the weight of the weapon and just how hard it is to use; their character would appear clumsy and off-balance. The more they used the great sword, the more professional their fighting animation. By the time they'd maxed out their skill with the weapon, all of their motions would be with purpose and precision.
Of course, this would mainly be relevant to melee classes, but it could also be done with mage types (especially if magic users were given more opportunity for close combat).
In this way, we wouldn't have to watch our character repeat the same 3-4 combative motions (saying it's anything similar to FFXI's combat animation system) throughout the span of our career with whatever weapon we choose.
Also, it'd be cool to be able to tell what "level" other players are at with their weapon/class by simply looking at the way they carry themselves in battle.
This wouldn't neccesarily have to be just how the character holds his/her weapon, but it could also be seen in stances and footing. The less experienced character would face its foe with a stance that is full of defensive holes while the master appears to be perfect in both offense and defense.
I know it'd take a lot out of the animation team to build in say... 9 race/gender-specific types of 5 different level-specific sets of animation/battle stances for each weapon type, but if they put their research in and did it right, I think it could add a nice touch of flavor to the game.