I may write up a more detailed post later, but I wanted to get this out there now.

Safari 4 Beta, like Google's Chrome has the right idea about tabs, but the implementation is horrible.

What's right:
The tab now encompasses the URL bar & navigation bar, which represents the contents of that tab.

What's wrong:
The title bar should be a title bar, not a container for tabs.
The tab now also encompasses the Bookmark bar, which is not in any way associated with the content of the tab, except to provide quick navigation to those pages. It does not change with regard to the different tabs, so why is it included as part of the tab?

Tabs, which usefull, still provide with unique UI challenges. I'm glad to see steps taken in the right direction, but it's still by no means utopia.