For the life of me I can't get the zoom feature to work on OSX 10.6 on my Max Mini. It's a fresh install, I have the wireless mighty mouse with the small grey scroll ball and the small wireless Apple metal keyboard.
I've tried enabling "Zoom using scroll ball whilst holding ^Control" mouse System Preference.
I also tried enabling Zoom in "Universal Access" in the System Preferences.
This did work in OSX 10.5, but seems to have stopped since I installed 10.6.
Yes, they have some crazy bug. I've been experiencing this too. Just open up the Accessibility preference pane, click Off and then click On, and it will start again. Not sure what is killing it.
Try changing the Zoom while holding to option in the Mouse panel of System Preferences. Perhaps there's a problem with using control on your system due to a conflict or somesuch.
OK, next thing to check is what screen resolution are you running your monitor at? See if you can zoom at a lower / another resolution. Perhaps the Mac Mini can't handle some resolutions.
I have no idea why, but this feature just magically started working again. One day not working, next day working. No reboots or changing configs or swapping batteries on mouse/keyboard.