Quartz 2D Extreme is once again available in 10.4.4, available in Quartz Debug, part of Xcode (the Developer Tools).
To enable it, select Tools: Enable Quartz 2D Extreme in the Quartz Debug menu.
[robg adds: The 10.4.3 update disabled Quartz 2D Extreme. Previous hints explain how to permanently enable Quartz 2D Extreme as well as how to enable it on unsupported Macs.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060125192805398