There are a lot of things one could say about Chuubo's, but my favorite part of it is quests. My Fate post talked at some of the issues I have with most advancement systems. Chuubo's doesn't necessarily do anything super-creative about the "more strength, bigger rock" problem (though relatively low skill caps and focus on new powers probably doesn't hurt). But what it does address is something I might call the "advancement/character disconnect", where the things at a meta level that advance your character are often unrelated to the character narrative or the actions your character would take to improve a skill.
D&D is the classic example. Want to learn a new language? Kill some goblins. If you're trying to put ranks in spellcraft because of your convoluted backstory and everyone being racist against psions, practicing every evening with the party sorcerer is irrelevant, you just need XP. Sure, there might be some text somewhere saying the GM can require you to do something to justify learning a skill, but whatever. And sure, there's roleplay XP, but that's really not a first-class citizen at all.
Fate's lockstep advancement, where everyone gets a milestone based on accomplishing something in the plot, has some advantages and disadvantages, but is pretty fundamentally similar. Both these systems work fine for adventurers having adventures, but they don't really support things like character development and meaningful scenes that aren't overcoming a foe well.
Before I get sidetracked into comparing the advancement systems of every indie game I can think of, let's circle back to Chuubo's. Chuubo's has XP, though on the "glass bead" scale, not the D&D "large mathy number" scale. But earning it and spending it are very different, and tied to quests. At any given time, a given PC can be on a number of quests, which could be anything from a project you're working on or a skill you're trying to improve to a literal in-world quest or adventure to something less directional, like having a secret hideaway or taking care of a sibling. Each quest comes with an amount of XP to complete it and ways of getting XP that are specific to the quest. (There are other character and genre-based ways to get XP as well.)
This, I think, does two cool things. It gives you, as a player, an ability to declare things your character is doing as meaningful or significant. Sure, in a D&D game, I can describe how Tslarc is spending his evening around the campfire carving a quartz statuette of a hypothetical cloud god, or how he wants to somehow get turned into a cat. Having those be official quests that he's on makes spending time on them feel meaningful, and helps establish some two-way communication with the GM on plot direction and character development. Secondly, it avoids the "fighting is the way to get better at everything" that's great in a dungeon crawl but awkward in less combat-centered games.
In some ways, you could argue, quests are a structured way to do "all XP is roleplay XP". But in the right game, that might be exactly what you want. I'm certainly interested to try it out sometime.