A propos of the new Reader feature of Safari 5, Derek Powazek just sent a note to Apple: Justified text decreases readability:
Safari 5's new "Reader" feature makes my site less readable by justifying the text. Flush-left text (aka ragged-right) is demonstrably more readable, especially when the rendering engine doesn't know how to hyphenate. You never, ever justify text without hyphenation.
One of his readers disagrees with him:
I prefer the justified text and was extremely and specifically pleased Apple made Reader this way. As I get older, justified text is infinitely easier to read as long as the column width is not so wide that my eye loses track of the left edge. Ragged right text just looks lazy and sloppy, to my eye at least. I realize I may be in a minority.
I see this comment as a sign that Apple will not fix this, because to the dismay of typography experts (and mine), most people out there without significant reading impairment cater to justified text for aesthetic reasons only. Those are Apple clients, and Apple will please them before the typography experts.
I have made this test numerous times: it's only when you point to someone how their eyes travel on a page and what constitutes an obstacle that they become conscious of readability issues.
You can make this test yourself.
Take attention-grabbing stuff on the left of a main content column, for left-to-right readers (or the reverse for right-to-left languages). When you read text and reach the end of the line, your eyes will travel back to the left in an automatic movement to fetch the left edge of the text column. If something is placed on the left of the text column, and is prominent enough to catch your eyes attention, they will continue to travel left and fly far more than necessary, then you will have to make an extra effort to realign them on the left edge of the text column to resume reading. And this for each line of text where there's something distracting on its left.
Most people will not notice this readability issue (until they get a headache maybe). But once you make them conscious of their eyes movement, the cognitive and muscular taxes imposed by the obstacle on the left become almost painfully visible.