I've done a lot of web development in my time and a lot of that time is usually sucked up in trying to make a site 'scale' well  - not in terms of dealing with vast quantities of users, but responding to changes in font size without the page layout going completely screwy.

Generally the user can change the font size on the fly to suit themselves, and as a page designer you really ought to cater to their whim. This means that you can't assume that your carefully setup sidebar links will always require just one line each, or that your box titles will always fit in the space available. It can be a nightmare to get right and if you have a very 'designed' page you often have to accept that it will only look reasonable within a certain font size range. Here's one of my blog posts unzoomed, looking handsome as always:

I've noticed that web browsers have increasingly been looking to solve this problem without troubling the poor page designers. Safari 4 Beta and Firefox 3 now default to simply scaling the entire page rather than just the text, though you can select a "Zoom Text Only" menu option to go back to the previous behaviour. By zooming every last pixel of the page identically, page layout and design are kept together and in the originally intended proportions no matter what, though any images on the page may start to look a bit fuzzy as they get zoomed up beyond their native size.

Here's that same blog post of mine with text-only-zoom and then everything-zoom in Safari:

 

You'll notice that Typepad have done a really good job of making their site text-zoom friendly, and with everything zoomed (and not zoomed quite so much) the whole page is too wide to be usable. Horses for courses I suppose – there are going to be cases when each method is superior and hopefully users (ones that care about zooming at all) will be savvy enough to choose what works for them.