Reader Joe Forbes' heavy-handed mousing is causing problems with Safari. He writes:
I am now using Lion with a Magic Mouse. Sometimes when navigating windows in Safari with the mouse the page zooms in. I have never been able to figure what I was doing to make it zoom or how to zoom out. The only way I have found to go back to the original is to close the window and re-open it. Can you enlighten me?
You're undoubtedly triggering one of Lion's gestures. By default, if you double-tap with a single finger, you'll zoom in on a Safari page element. To zoom out, double-tap again with that single finger. This is the Smart Zoom gesture.
This is one reason I find the Magic Mouse a less-than-ideal input device under Lion. Because it has no physical buttons that register an intended tap or touch, it's possible to accidentally trigger gestures, much as you seemingly have. Thankfully you have options.
First, familiarize yourself with Lion's gestures. You do this within the Mouse system preference (or Trackpad system preference if you're using that device). Just hover your cursor over each gesture and you'll see a helpful video that demonstrates how to trigger the gesture as well as shows you what the gesture does. Knowing what a particular tap, click, or swipe can do will help you avoid accidentally triggering gestures.
Secondly, turn off those gestures that get in your way. If you can't avoid zooming in on page elements when working in Safari, switch off Smart Zoom. If you accidentally move between pages, turn off the two-finger side-to-side swipe gesture that initiates this action.
I understand that gestures is one of Lion's marquee features, but you likely got along just fine without them when using Snow Leopard. If you find them distracting, there's no shame in switching them off.