To me, a more interesting question is which skills will your character never use. I play a mage type, and using a weapon, or at least fists, is sometimes unavoidable; that doesn't stop you being a mage. If, however, you play a mage who refuses to use conjuration, that actually says something about your character.
I completely agree.
I'm predicting a much greater flexibility to customize each characters as a result of the changes to the skill system and perks.
For the first time in any TES game, I'm looking forward to playing some warrior, assassin and archer characters that won't use any magic whatsoever. likewise, some mages that will focus on one or two schools of magic.
Certainly over the course of a very long playthrough, a few lesser used skills will eventually increase, but there will be some we absolutely don't use at all, unlike Oblivion.
And with perks we have the capacity to specialize completely in one skill, getting all of the first 20 perks from the Archery perk tree, for example, or 2H, or Illusion, etc.