Late to the thread, but my interface gripe on this has to do with where one is looking!
The old search box (Google, Bing, or Yahoo) was on the right-hand side of the screen-- right above where new tabs would be added. That meant you could focus on one part of the screen. Now, I have to shift my gaze back and forth. No biggie at one level, an irritation at another. I have no problem with changes in interface and design-- so long as they keep an option to restore the old interface for those who want it!
Incidentally, I tried that Google search bar extension and all it seems to do is add yet another horizontal tab bar across the screen with the box way on the left-- even further over than Safari's!
Aha! Just thought of something... if they'd let us resize the search/URL box, and/or position it where we wanted it, all would be fine (or, at least, better!).
The only other solution I can think of is to put as many icons as possible on the left-hand side of the search box to move it over some.
Perhaps the solution is to permit us to have two instances of the search box... that doesn't work!
Anyone know of another extension that brings back the old search box?