I'm sorry to see that requests of power users are getting ignored over and over. Doesn't it occur to the IE team that the great success of Firefox in the non-geek community is driven by requests from power users and subsequent implementation by FF developers?
The decision to move addressbar and tabs bar on one row is an awful decision. Your telemetrics must be misleading. From my experience, most "ordinary" users have much too many tabs open and not "less than five". They also tend to leave their IE running for days and not close any tabs. A typical behavior is to search at Bing or Google and then open several fitting links in a new tab. This way people easily go to ten or twenty tabs in short time. I have hardly seen a browser (any type) open with less than ten tabs on *any* user's PC unless it was opened fresh. So, something with your telemetrics is clearly wrong.
One user mentions that tab groups were a complete waste of dev time if your telemetrics were true. Indeed! If people were behaving like you think tab groups would be useless, throw them out!
There's indeed room for streamlining the UI and toolbars. For instance, putting address bar, Favorites bar and command bar on one row may make sense for many people. Or using the title bar for tabs or display of the (ooops) title. It's just ridiculous that IE9 has a title bar that is almost empty. Do you really think that is what people want? An empty title bar and tabs where they can't read the title? Unbelievable.
One of the factors of why IE6 has been such a great success was its UI flexibility. One was able to drag the toolbars in almost any "shape" and layout, including putting them all on one row (remember, that was before tabs were added in IE!). Ever since the UI flexibility was degraded by the IE team with every new IE version (actually it was decreased much with IE7, increased a little bit with IE8 and found its low point with IE9 now). Have a look at Firefox during that same time. While the flexibility in the IE UI degraded during this time the UI flexibility in Firefox increased. And the market share and popularity of Firefox increased, too. Think about that.
One user posted a screenshot that shows that putting address and tabs on two rows doesn't necessarily give a better usability. Right, not with the layout shown on that screenshot. I wonder if it never occurred to the IE team that one can move the tabs bar to a row of its own with IE8. I don't see that any other solution could top this. Unless one were able to display the tabs in the title bar or vertical (at least on a widescreen). Why is it so hard for the IE team to understand that the IE9 solution is a usability nightmare?
Thanks for listening.
(Btw, that screenshot shows another problem with tabs: the ... abbreviation marker. That marker is useless. It takes valuable space that could be used to display yet another one or two characters. If you want to cut space start there!)