Here are some of the visible prominent changes in Safari 5.2
Reader has always been, in my opinion, one of Safari's under appreciated talents. After all, the feature to turn cluttered and clunky multi-page articles into a single paged neat and ad-free article with the perfect layout and font-size has definitely earned a spot on my list of favorites.
What was previously a small black button that would appear upon availability is now a permanent and prominently visible button next to the URL bar. When Safari detects an article on the webpage, the reader button automatically turns blue. Click it to read in a clutter-free and clean environment space.
Unified Search and URL Bar - The google search bar on the right corner of the safari window has now been integrated with the main URL bar. ( Possibly an idea taken from chrome ). To google something, simply start typing.
Tabs on Safari now expand to fill the tab bar no matter how many tabs are open. Even if you have just two tabs open, Safari will expand them to fill the entire space which makes viewing and switching between tabs a breeze.
The 'http' before the site URL no longer exists.
Apple has grayed out the everything after the root domain making the root domain far more prominent.
Here are the some other changes in Safari 5.2
Passwords can now be 'Autofill-ed'. Safari asks you if you want to save the passwords for any websites which require it. If you choose to, it will automatically appear in Safari's preferences under the new 'Passwords' tab
The options for default font and font size seem to have vanished.
Also, new privacy options such as "Tell websites not to track me" have appeared.
While these changes seem to be largely for the better, only time will tell how they actually work in practice.