iA's Writer app for the iPad has been on my home screen since it launched, and it's one of the apps I bring up when people ask me what brings me to carry a giant iPod touch in my bag. In an age where it's not at all weird for someone who writes for a living to stare at two or more monitors displaying tweets from hundreds or thousands of Twitter users and RSS feeds from hundreds or thousands of websites/blogs in real time, iA Writer is an infinite number of steps in the opposite direction. The effect on my ability to craft words has been nothing short of ridiculous.
There are no settings, just writing. Formatting is handled for you using Auto Markdown. Everything can be driven from the keyboard (and you can ask any digital audio/video professional how essential key commands are for maintaining a state of flow). Focus mode greys out everything except the sentence you're writing, so you can concentrate on writing, instead of getting distracted and tweaking the cadence of the previous paragraph.
If you write, or want to write, at all, try it.