The Magnifier came on for me and I was annoyed. So rather than reboot, I went to the web to see how to turn it off. I see others have the same issue I had.

In my case, the magnification was not caused by Vista since the control panel -ease of use magnifier checkbox was not checked.

I found that my mouse software was the issue. I have the wireless intellimouse explorer 2.0 from microsoft. So under start-all programs- microsoft mouse-microsoft mouse, I noticed that the small thumb button is set to start the magnifier (and turn it off too). I am changing this setting because I really don't want to accidentally turn that on again.