Saloni Mira Rai, a program manager on the Internet Explorer 8 Layout team provides a walk through of the changes in Zoom for Internet Explorer 8:
Zoom lets you enlarge or reduce the view of a web page to improve readability. The feature is particularly useful on really large and really small displays, allowing for scaling of content while maintaining the intended layout of the page. The second iteration of the zoom feature (first shipped in Internet Explorer 7) focuses on improving the existing experience by providing a higher quality, more predictable, and persistent zooming experience.
What You Can Expect
As you zoom, IE8 will size the text and images and reflow the page to make it easier to read. You will not see a horizontal scrollbar for most mainstream scenarios. It’s easier to show than explain, so here’s an example:
Zooming the IE Blog to 150% in IE7 looked like this:
Notice that text moves off the screen and a horizontal scrollbar appears at the bottom of the screen.
Internet Explorer 8, IE8, Zoom, Features