Look to the right, and you may notice Safari's first major missing feature: RSS. It looks as though Really Simple Syndication was just not simple enough for Apple; the company has excised RSS entirely from Safari (and from Mail as well), leaving feed-parsing to external applications such as NetNewsWire or Reeder. If you have such a program installed and attempt to type in or click on a "feed://" address, Safari will automatically punt you to your respective program; otherwise, it displays an error.
In place of the RSS button and old search bar, Safari has added a giant button for Safari Reader, which highlights the text on a page for an easier browsing experience. When browsing a page where Reader can be used, the button will be blue; for all other pages, it's grayed out.
Unsurprisingly, several changes made in this version of Safari relate to user privacy, a particularly hot-button issue in recent years. There's now a "Tell websites not to track me" box under Privacy, along with a setting to "Allow search engine to provide suggestions," which relates to Safari's search capabilities. A new Passwords section lets users see each website they've saved information for, along with their usernames and obscured passwords. (Passwords can be revealed, but only after several rounds of user authorization.) You can delete individual stored passwords, or remove every one, if you so choose.
There were two other things of note that I found during my preferences exploration. Safari no longer offers an option to set default fonts and sizes (though you can upload a style sheet or force the browser not to show font sizes smaller than a certain number); as the Web relies more on CSS styling, this makes a certain amount of sense, though I'm sure there's a contingent who won't be so happy about it.