Looks like OS X can preview fonts now, but in an unlikely place. You do remember being able to double-click a font and have it preview in the 7.5 to 9.x Finder, right?
In 10.2, open a Cocoa app that uses OS X's text services TextEdit, Mail, etc., and open the font panel (usually command-T). In the "Extras" pop-up, there's now a "Show Preview" option! Yay!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020907082142672