As a software engineer, I outline a lot in preparation for writing code. I'm currently using OneNote, and the features I find most important are:

• keyboard shortcuts (e.g. ctrl+shift+L to go into bulleted-list mode
• smart list-making (e.g. hitting enter makes another list item; hitting tab indents the current list item)
• checkboxes -- to mark off what I've done and what I need to do