|-- _config.yml
|-- _drafts/
| |-- a-draft-post.md
|-- _layouts/
| |-- default.html
|-- _posts/
| |-- 2013-05-10-a-published-post
|-- index.html
Normally (and on GitHub Pages) Jekyll will ignore the posts in the _drafts folder, publishing only the posts in the _posts folder. If you run Jekyll locally with the --drafts flag (e.g., jekyll serve --drafts), Jekyll will include any posts in the _drafts folder, just as if they were published post (but don't worry, only locally).
Now that GitHub Pages are limited to 10 builds per day, is it safe for me to assume that committing to the _drafts folder does not trigger a build?