I zoom most of the sites I read mostly due to the number of characters per line. When it is greater than 120-140, I can't focus on the line I'm reading.
And that is by the way another reason I love fixed size layouts: you can zoom them however you like.
Re: fixed size layouts, I don't get this. You might be able to zoom these on the iphone, and scroll around the page easily with your finger. But I find fixed sized layouts can be a pain. Preferring fluid. Because at least I can resize the browser window - to get a good line length etc. It's annoying if you do zoom in and the text flows out the side of the browser. I don't enjoy side scrolling.
And that is by the way another reason I love fixed size layouts: you can zoom them however you like.