I am a PhD student and have been looking for an application like this for years. Word is too unpredictable, bloated and constantly messes with formatting, styles etc. Scrivener helps me structure, organize and visualize my writing in a way that helps me be more effective.

There is a relatively minimal learning cure compared to similar apps on the Mac. Despite the application's apparent simplicity, it offers a rich set of writing environment including an excellent full-screen mode.

The user forums are among the most helpful I've seen and the developer is responsive and is also a stand-up guy.

It is future-proof because all text is stored as rtf files in the application bundle, accessible via OS X and it offers multiple export options, including rtf, rtfd, html, latex, pdf (via the OS X print menu) and multi-markdown. It also plays well with DEVONthink.

Highly recommended for academics, writers, researchers, poets and anyone else who need to actually "write"!