This is EXACTLY what my writing workflow needed.

I was, literally, in the process of setting up an index card system for my story (seems too presumptuous to call it a novel). One stack for character notes. Another stack for settings. Five top-level story arc cards, each with 4-5 chapter cards underneath, each with some number of scene cards underneath. I was dreading the book-keeping involved in keeping these cards synced with the actual document (which I had been keeping as a single massive document in Word, as clumsy as that is).

Instead, I found Scrivener. Instead of index cards on a massive cork board in my office, Scrivener puts all that next to my chapters and scenes. So, instead of rearranging scenes on a corkboard to make it work, then translating those changes back into the main document, I just do it all directly in Scrivener. Plus, unlike the cork board, I can attach keywords (which characters are talked about or in a scene, which settings are described in a scene, etc) to scenes, so I can do a search for any of my characters, select the scenes found, and read through that character's development to watch for any inconsistencies or unexplained changes.

Like I said, I've only been using this for two days, so it's still a bit early to really "review" it. Still, I am seriously impressed with what I see, and, assuming no a major flaw crops up in the next week or so, would easily pay twice the asking price for it!

Finally, a few notes about my process and how Scrivener fits in:

I'm a "casual" writer, writing in small snippets of an hour here, a half-hour there, primarily for my own enjoyment. As such, I tend to forget more of what I write down than I remember. Organization is key to allowing me to produce something semi-coherent to show for this.

I use DevonThink as well, to collect interesting facts and ideas which might eventually make it into my writings. I might eventually transfer the pertinent ones over to the Scrivener Research Binder for easier access while writing, though I think right now they'll be staying in DT. I don't see any need to have my particular "research materials" and notes up on screen while working in Scrivener; they're more idea-sparkers than referenced sources. Your mileage may indeed vary.

I also use OmniGraffle to jot down floorplans and such for various scenes. I'd like it if those diagrams could go into Scrivener (ie, subsume the graffle package into its own package structure, and launch OmniGraffle when I double-click that file in the binder) but they can't (yet?).

In Scrivener, I have keywords for settings, characters, and themes. For each of these I also have a file in the "Research" section which describes that setting/character/theme, which gets the keyword attached as well as related keywords. So, if I want to see everything that's happened in the "Gymnasium", I search for that keyword, and at the end of the story snippets I have a synopsis of what the Gymnasium setting looks like and how it is important, etc. This should make it easy for my "synopsis" to be kept close to reality. The next time I come across the Gymnasium, then, I just refer to the synopsis to refresh my memory of how things are laid out, etc.

Once I'm done with the "writing" part in Scrivener, I'll export it out (to Word or Mellel) and print out the format-fixed copy.