Sebastiaan hits the nail on the head that this is not just a faster browser with some noticeable interface changes. Yes, the major features are obvious, but there are many subtle touches surrounding those features which make it a whole new ‘experience’.
I am the most sad about the loss of the address bar’s blue progress indicator. That was one of the first UI features I noticed about OS X on my friends iBook over 5 years ago, and is the missing feature that throws me off the most in Safari 4.
And what’s my favorite new feature? CMD+OPT+F (UPDATE: Apparently this feature is old school. Something that would have been nice to know earlier. Next thing you know, I’ll find out that this same feature works in Mail too… Doh!)