I've been keeping my resume in Markdown form in a private Gist for as long as I can remember. This approach has stood the test of time despite Markdown offering zero intrinsic support for either document structure in general, or the task of writing a resume in particular. In that, it's a good light-weight format that doesn't really get in the way. The plain-text nature makes it a good choice for VCS. There are lots of ways to turn Markdown into a user-friendly format like HTML or PDF. In short, it does everything I need and nothing I don't.
My rule of thumb is to keep it simple and convenient. Compared to this, most other approaches I've seen - especially ones that try to shoehorn everything into some kind of data model - smell more like overengineering than anything else.