Mac OS X Tiger (10.4) had an minor update (version 10.4.8) not long ago and while the changelog seemed pretty uninteresting on the most part, there was one unannounced feature that's pretty cool - Zoom Using Scroll Wheel. If you've already updated to 10.4.8, you can try it out for yourself now by holding the Ctrl key and scrolling up the mousewheel. Cool, yeah? You can still do whatever you want in the magnified view (I took a screenshot) so it's not simply a cheap static magnification (just as Expose windows aren't static screen captures of your open windows).

Screenshot of Digg taken with Mac OS X new zooming feature