The most popular "writer's distros" seem to be derivatives of Puppy Linux, a distribution designed to cram as much useful stuff into as little space as possible. It runs most anywhere -- from a live CD, a flash drive, across a network, etc. -- and makes older PCs highly workable. (Best feature: You can boot from a CD, and then write any changed/saved data back to the CD when you're done.) KwillerPup is a customized Puppy distribution with some author-specific software like yWriter, a free word processor by a novelist and for novelists. (From the same author and also included in the same distribution: Sonar, an application for tracking submissions of work to different publications.)
There were other distributions, but they regrettably seem to have fallen by the wayside. GhostWriter was one such project, but it's vanished -- the site where it was hosted is no more. Another distribution which caught my eye was NaNoWriMo Linux, but unfortunately it also hasn't been updated in quite some time. NaNoWriMo, incidentally, stands for National Novel Writing Month, a voluntary project held each November where the participants all try to bash out 50,000 words in 30 days. (The vast majority of my most recent novel was produced as a NaNoWriMo project -- although, I confess, it was written in Word 2007 on Windows Vista. Shame on me!)
Distributions like these also are perfect for the student or fledgling young author who's been given a hand-me-down notebook and wants to get the most out of it with the least effort. I'm curious to hear from folks who use a Linux distribution as a creativity tool as well as a productivity tool -- whether they're using any of the above distros or something completely different.