I have been trying to gather objective feedback/response on the design of the Fluent UI ('Ribbon') interface. Apart from one study by Forrester which was commissioned by Microsoft anyway, and various rants or opinions on every blog or website imaginable, I haven't really seen anything specific or objective about the design from a usability or long term productivity evaluation. This website gathered some survey on Excel 2007, but I couldn't get any meaningful usability analysis or whether it was just a short-term effect of getting used to the change.
Also, other software developers are also adopting the ribbon UI as a result of the Microsoft interface design change (e.g. Nitro PDF, Autodesk) and therefore now it is also a case of trying to conform to a known standard rather than purely based on UI research and analysis alone. Is there any objective research in this area that can be referenced at all that anyone knows of?
I feel like from a professional point of view, there still hasn't been any definitive study on this that allows an objective decision to be made about implementing the design, or any follow-up to gauge the impact of the change. Furthermore, comparison of productivity between new computer users starting from the ribbon interface versus people who started from the traditional menu interface is not available either even after such a long time. I think this shows the lack of objective research when it comes to this topic.