Reading web pages on the iPhone is a very different experience than reading them the desktop version of Safari. Some things (like entering text and so on) are inevitably slightly more awkward because of the onscreen keyboard. But there's one thing in particular that I'd like to see in the full version of Safari: zooming in on page elements. For those who haven't used Mobile Safari, each page is initially displayed full width, which for most pages results in tiny text, but means that you can see at a glance the layout of content on the page. The magic comes when you double tap a page element like a column of text: it expands to fill the entire width of the page, which for most pages I've tried makes it perfectly readable. It also -- and this is why I want it in desktop Safari -- removes any of the other distractions on the page. This is perfect when you're reading typical sites with sidebars and other content at the side of the page, and is particularly good with online news sites where you have flashing adverts and other distracting elements to either side of the content.
It's the web browser equivalent of 'full screen mode' on a text editor, and I'm rather addicted to it. So much so that I tried double clicking a column in desktop Safari earlier today to concentrate on what I was reading.