Mac users also have a number of distraction-free writing apps to choose from. The granddaddy of distraction free writing tools is a handy app called WriteRoom that creates a full screen word-processor that hides all menus until you need them later. While WriteRoom has updated over the years with a lot of exciting features (there's an iOS version now that syncs well with the desktop app) it's also $9.99 in a field where almost all of the competitors are free.
I prefer OmmWriter for my distraction-free writing in Mac OS X; not only does it help me focus and be more productive, it also has a few customizable themes (with more available in a premium version of the software) along with some soft ambient noise tracks to drown out any distracting outside audio.
Last (but certainly not least), Linux users and any Windows or Mac users unsatisfied by other offerings should take a look at the cross-platform FocusWriter, a great little full-screen text editor that supports themes and tabbed document browsing in addition to the usual hidden menus and keyboard shortcuts.
Distraction-Free Desktop Apps
There's no reason to limiting the distraction free philosophy to just your writing tools however. There are also plenty of great tools to eliminate distractions from your PC desktop and stay more productive.
Mac users know that lots of Mac OS apps commandeer the entire screen while running in full-screen mode in the newest iteration of Mac OS, Lion. The support for full-screen apps has made many of the Mac's most popular applications (Final Cut, Photoshop and other video/music/image editors) distraction-proof by default. If you've got Lion installed, make sure check for a new Full-Screen App icon in the upper right corner of your application window. If you can, hit that button to turn your favorite app into a distraction-free zone.
Of course not all apps will have full-screen support and for some situations you'll still need to run multiple windows at once. If that's the case you can still minimize distractions from other apps with the help of Backdrop, a handy little app that will let you hide not just other applications but also your computer's desktop when you're trying to get work done in an application.
Windows users may be interested in Ghoster, a free utility which dims all your windows except for the currently active one to help you stay focused. It won't actively block notifications from programs like AIM or TweetDeck, but you can probably shut those down on your own if you need to get some serious work done.