In chapter 15 of MSCD and in this May 2007 post (which has attracted 32 comments) I explain why using ragged right margins makes word-processing documents easier to read. It’s a no-brainer—you may think that full justification looks “professional,” but typography experts are unanimously in favor of ragged right for word-processing documents. (Books and other works prepared using typesetting software are another matter.)
When you’re looking to shift entrenched positions, repetition can be helpful. So if you’re not convinced of the righteousness of ragged right, I suggest you check out this post on slaw.ca by Simon Fodden. (I learned about it from Ray Ward.)
Simon takes the opportunity to point out that it would be best to use one space, not two, after punctuation. So say all typography authorities I’ve consulted; I discuss that too in chapter 15 of MSCD and in this October 2006 blog post.
In all things relating to typography, bear in mind that people like what they’re used to. So if you’re inclined to fight tooth-and-nail for full justification and two spaces after punctuation, bear in mind that your own habits are less relevant than the views of typography professionals.
And bear in mind also that these habits are not hard to break. Once you make the change, you realize that the sky hasn’t fallen and that, in fact, life is a little simpler.