FWIW I haven't seen any serious scientific study to support the contention that a ribbon interface (at least as has been implemented by Microsoft) is more effective or productive than the classic drop-down menu system.
-40hz
I remember when they were designing the new interface, Microsoft did a series of extensive tests which have shown that the ribbon is easier to use. I know there was a very long video (2h or something like that) showing how they tested it and why they settled for this interface.
Because that's all it really is at this point - a 'look.'
-40hz
IMO you are seriously undervaluing how important the user interface is. Apple has repeatedly shown how important the look and feel of stuff (software and hardware) is for people.
What users do appreciate, however, is a well designed interface. And there's nothing to show them a ribbon is superior. So I don't think the absence of a ribbon is any disincentive for your customers. I have yet to hear any reviewer recommend not buying an app just because it didn't have one.
-40hz
That I surely agree with you. IMO what you must decide is if the ribbon is good for you, as it isn't good for every type of app. I think Ath's links should be very helpful with that, at least I found them very interesting.
Also, but this is only personal taste, please avoid at all costs non-stantard interfaces

(and I hate what MS has done with the title bar of windows in office :/ )