The placement isn't necessarily the issue. My issue with the new tab bar isn't that the tab bar is above the address bar — I use Opera at work and I think tabs-above works fine — but that the tab bar is part of the title bar. It confuses the functionality of both:
- You can't drag anywhere in a tab to reposition it or move it to another window — you have to grab a little icon on one side of the tab.
- You can't double-click anywhere to add a new tab (because double-clicking the title bar minimizes a window).
The extra ten pixels of screen real estate that you gain by merging the two doesn't make up for the design issues it introduces, IMO.
Also, they further muddied the UI by using the same icons for different things: + for "Add bookmark" and "New tab", and the lined triangle for resizing the window and reposistioning tabs. Especially with the lined triangle appearing near the top right corner, it wouldn't be unreasonable for users to confuse it with the same icon in the lower right corner.
I don't mind the new can't-get-rid-of-it Add Bookmark button in the address bar, but it seems arbitrary at best. If someone wanted an Add Bookmark button to the left of the address field, they could always add it there; but if someone doesn't, you can no longer remove it (without hacking the prefs).
Same goes for the Mobile Safari-style Refresh/Stop button, but it is a little less arbitrary. On one hand it doesn't make sense to remove the flexibility of customizing the tool bar as you want, but on the other, it is one more way to make mobile & desktop Safari more similar. When they changed the Mobile Safari search field style to be more like desktop Safari, I initially didn't like it; but over time, I found I didn't care much one way or the other.
The omission of the blue progress bar in the address field is odd, too, but as others have poitned out, it's mentioned on the Safari webpages so perhaps it's just a beta fluke.