As of 10.4, I think, Apple started making plists in a binary format instead of XML. Though they had their reasons, it was a real pain if you just wanted to get a very quick look (no pun intended) at the preference settings, because it meant that you either had to convert the file to XML using plutil, or open the file in Property List Editor, which is not well suited for browsing settings at all.

But in 10.5, Quick Look displays binary plists in XML on the fly, so you can now select a bunch of plists, launch Quick Look, and view page after page of beautiful XML with all the navigation features that Quick Look offers. It's a very useful way of helping one assimilate or drill down into a system's configuration.