Classes: I think the best use for Themes would be to make separate classes. A "samurai" character would be created by starting with the Fighter class and then adding the Samurai theme. We don't need fifteen flavors of Fighter; we just need one fighter with fifteen themes.
Racial? That might be pushing it. Backgrounds maybe, but not themes. Themes should be stuff your character learns and trains to do, and backgrounds should be stuff that describes where your character came from.
Combat (Weapon Style): absolutely. This is the most elegant solution to the "flavor of ranger" debate going on in this forum.
Combat (Tactic): I'm not opposed to this, as long as "tactics" isn't some sort of code word for "superhero superpowers of super-awesomeness." Maneuvering around the battlefield and disarming your opponent is one thing; turning your sword into a flaming lightsaber by kissing your bicep and yelling is another thing altogether. (But if you *must* have the bicep-kissing lightsaber-summoner, I would prefer it to be in an easy-to-ban Theme instead of a ubiquitous core character class.)
Combat (Roles): I don't care for the idea of "roles." Back in the day, people would complain about being forced to play a cleric because "the party needs a healer." Nowadays, people complain about being forced to play a fighter because "the party needs a defender." I think they should leave roles alone, and leave it up to the player to decide how his/her character fits into the game world.
Prestige/Paragon/Epic class: I like it. Something like, "every 8 or 10 levels you get to pick another theme" would work nicely. It would make multiclassing a lot smoother, anyway.
Templates: Eh, I'm not sure. I mean, it's a great idea, but we don't know enough about the monsters to be able to tell if this would work. Pencil me in for "maybe" here.
Spell school/Specialist Casters: Sure. I consider this category to be "weapon styles for non-fighters."
Templates: Not sure why it's listed twice.
Other: I think that themes would be a great way to handle item creation as well. An "alchemist" theme could give a character the ability to make alchemical preparations and potions, in sort of the same way that the Healer theme works. An "artificer" theme could let a character create magical weapons and armor. It always bothered me that only spellcasters could make magical swords. Most wizards don't even know how to use a sword...