Where do you draw the line between what goes in a Notes app and what goes in a writing app?
If you jot ideas in a notes app, when does it graduate to the writing app?
If you just use one app for everything, what do you use and why?
Also, what’s working well for you? What is bugging you?
I’ve recently transitioned to using iA Writer as both my notes app and my writing app. It’s working quite well so far.
I take more notes than I do write “formal” documents – meaning something that needs to follow a template, or needs pretty formatting for someone else’s consumption.
If I’m writing a formal document I usually keep the outline on the first page, work from it, and then delete it when I get to a stage in writing that is focused on editing and filling-in details. I don’t use Word’s or Pages’ outlining features – they are pretty much useless for the writing I do.
If I “jot ideas in a notes app” they are usually handwritten ideas, or a maybe a mind-map, or maybe for bigger or more complex things a concept map developed in Tinderbox and/or Curio. Only rarely do I move those things into Word or Pages – where I do most of my formal writing.
I also do a lot of PowerPoint decks because my clients are obsessed with this format(1) – these start with an outline then the pages get fleshed out, graphics created in Visio or elsewhere, etc. PowerPoint decks get a lot of collaborators putting their hand in.
I produce about 15,000 - 20,000 words / week for clients – counting all the revisions and collaborations – and these processes have worked out very well in my environment.
(1) probably contributing to the ultimate demise of civilization, of course 
What’s the difference with Drafts and iA writer??