The best personal note-taking facility of which I'm aware of has nothing to do with note cards, notebooks, tape recorders or PDAs. It does need a web server and a willingness to do some typing, but I find that a personal wiki, set up for yourself and yourself alone, can perform wonders when used as a place to jot down thoughts wherever you are (especially if that happens to be a computer-rich zone, like a college campus), and is close enough to a mind map all by itself to be very useful as an organizational tool.
The first thing that makes wikis great for this is the simplicity of markup. To someone who either doesn't already know HTML or wants to read the unadorned source text, wiki markup is about as close to ideal as you can get without going WYSIWYG. Italics are imparted by double single-quotes, boldface by pairs of underscores before and after, and lists are made by merely adding asterisks to the beginning of lines. Start a new paragraph with simple blank lines. It's not perfect, but it's very easy to get used to, and when you're getting down ideas on the cusp of inspiration it's important not to get too bogged down by markup… or by sorting through pages, or fiddling with a pencil, or making sure you have room for further notes on a topic, as with a physical notebook.
The other useful thing is the very Everything-ish creation of new pages and links between them simply by putting brackets around them. I keep a PHPwiki in order to keep track of various pieces of information related to the novel I started last November as part of Nanowrimo. Whenever I'm writing something in it and suddenly realize I need a new character there, I just put his or her name in brackets.
When I'm done editing the page, it'll have a little question mark after it. Clicking on that takes me to an empty window perfect for filling in anything I care to add about that character. My mind tends to jump from topic to topic like this, so it's ideal for producing large amounts of content, even if it won't necessarily be contiguous, or even appear, in the final work. At the end of the page I add the WikiWord CategoryCharacters, which simultaneously links to my character list page and adds the new page to it (courtesy of PHPwiki's BackLinks plugin). Very nifty! And it even saves regular, automatic backups of old versions of pages, in case I need to get back to an earlier vision of some character or event.
My Nanowrimo project got me off to a very rapid, very frantic start, but such was the rate at which I was forced to produce that afterwards I found myself, for the second year in a row, in a profound slump. It is difficult to keep that kind of pace up for long, especially since, at that speed, it's easy to get yourself turned around and contradict things you wrote a scant week before. Worse, promising story concepts passed up days previously tend to get drowned by whatever the current focus has to be. A couple of days consolidating with my wiki has produced a list of characters and places, described and cross-referenced with each other, that seems certain to bear fruit in the near future. Powering forward through a story can only take you so far – sometimes, the trick is, to meander sideways, even backwards through the mindspace you’re trying to examine. For this type of creative exploration, a personal wiki is among the most useful tools I’ve seen.