If you're running the WebKit version of Safari, however, you can activate full-page zooming using a simple Terminal command. Thanks to pamon for emailing me a pointer to this page on the Surfin' Safari blog that reveals the Terminal command. Quit Safari and WebKit, then enter this command in Terminal:
defaults write com.apple.Safari WebKitDebugFullPageZoomPreferenceKey 1
Launch WebKit, load a page, then experiment with Command-Minus and Command-Plus (technically, Command-Equals). You should see that all objects on the page are being resized, not just text. Note that Safari, because it uses an older version of the WebKit engine, won't be able to do full page zooming, even after running the above Terminal command. To reverse the settings, reverting WebKit to the "text only" zoom mode, repeat the above command, but change 1 to 0.

