Firefox 6 and Safari 5 now hyphenate. In theory this means that you can now justify blocks of text so they’ll look like the neat, square paragraphs in most (all?) printed novels, sans the rivers that
text-align: justify normally generates.
Leaving aside the fact that justification still doesn’t work that well on the web, I’m scratching my head as to why you’d really want to do it. True, it looks a little neater than left aligned text, but I can’t see any readability benefits (quite the opposite). Words are meant to be read, not just looked at.
I’d guess that justification works in print because its a lot easier to fine tune spacing and therefore hyphenation. And there’s no chrome to distract you from the text itself. But neither apply to web pages.