Another somewhat hidden new feature is the ability to use the Undo command (Command+Z on Macs, Control+Z on Windows) to recover a recently closed tab. You can also reopen recently closed windows from the History menu, although that feature was there before.
The most overt new feature is called “Reader”. When you load Web pages that contain multipage articles, the Reader button appears within the address bar. Click it and the articles content will appear above the page itself so that it’s easy to read. More than that, the text will appear without all the ads, links, and extraneous stuff that clutter up a Web page, and every page of content will be available right there (although, in my experience, it took a few seconds to load the rest of the article).
Similarly, when you’re in private browsing mode, a “Private” button appears within the address bar. This is useful if you enable privacy but later forget to disable it, and wonder why your other history isn’t available.
If you’re reading this post, you’re probably somehow involved with Web development or computers or whatever, and are likely to upgrade to Safari 5 quickly, regardless of what it has to offer. But I think that what companies put out in their latest browser versions provides a good insight into where some of the Web development leaders think the Web is heading.