Believe it or not, I've actually been asked quite a few times how I go about writing posts and felt compelled to share the answer with the rest of the world (as I often do).
My current text editor of choice is TextWrangler, which I've written about before. As I get an idea of something I want to talk about, I open up a new document in TextWrangler and immediately save it to a folder I call "scratch," which is for these posts and whatever other mind-fleeting thing I feel the need to jot down before I forget it; I give the document the name of whatever it is I'm writing about. TextWrangler keeps all of your open documents in a "drawer" to the side of the editing window and lists them in alphabetical order by name. I currently have 23 documents open, 15 of which are future posts. I've also created a shell script that syncs my local "scratch" folder with a folder on my webserver every couple of hours so that I always have access to my posts.
There are two advantages to this setup. The first is the fact that I can see, at a glance, all the posts that I'm currently writing or plan to write. The second is that if TextWrangler crashes (it never has) or I need to reboot for some reason (and close the application), I can easily get back to where I left off; I simply open TextWrangler, highlight my entire "scratch" folder in the Finder, and drag these items over to the TextWrangler icon in the dock.
In conjuction with TextWrangler, I also use John Gruber's Markdown, a plain-text formatting syntax. Initially, it was lost on me the need to learn John's syntax given that I'd been proficient in web markup for 10 odd years and hadn't really 'thought' about it in a very long time — it had become as natural to write as English — but over time, and especially for longer, more involved posts, Markdown became indispensable and now I can't imagine writing without it. It makes 'pre-markup' plain-text much more readable. Period.
Back to studying for Patents, my last law school final of the [academic] year.