The question for Zenimax: When you say "one costume slot", do you mean account-wide or character-wide? Can I make one costume for each character I have individually or just one costume period that they all have to share unless I buy more slots?
I myself only play magicka characters (and one tank), so for me, most of my transmogrifying is going to be based on picking a robe and shoulders. All of my characters are Argonian, so I'm still very unlikely to wear any kind of head piece, and the staves (I'm assuming) are still not really going to be capable of changing the color of (I will hopefully be wildly wrong about this and Zenimax will make staves actually take bright colors when you dye them instead of it just putting a dull color on it).
As for my tastes, I've always been a fan of Ye Grand Enormous Shoulders on mages, so I'm definitely going to be wearing my shoulders in Heavy on all of my characters, don't know what style yet.
I'm going to be making my magicka NB look as evil as I can, with a black, purple, and mauve color scheme, big pointy shoulders and all. My magicka DK is going with black as well, but with red, orange, and yellow accents, perhaps not pointy shoulders on him. I don't have any idea what to do for my healer yet except for a white, gold, and aetherial blue color scheme.
What are you all planning to do with your costumes? Styles, armor types?