If you haven’t seen this functionality yet then I should explain this is more than simply scaling the text size. Zooming scales the entire webpage (graphics and all).
The idea, originally invented by Opera, is an excellent one. Generally speaking it allows the user to scale any site without breaking the design.
It works particularly well for fixed width sites as it allows the user to expand the design to fill the screen when running at higher resolutions.
Not perfect, but pretty good.
However, the problem comes with scalable sites. Because these already fill the whole width of the browser window, as soon as you begin to scale the content on the right of the page gets pushed off screen like so:
This wasn’t a problem with traditional text resizing because only the text changed size and not the surrounding layout. This new approach is actually a step backwards for the accessibility of scalable sites.
Although it is possible to just resize text in IE7, this option is nowhere near as prominent as the zoom function and so will almost certainly become obsolete. The question is, will this cause scalable sites to become obsolete as well? It will certainly make me think twice before suggesting them to clients.