The UI, is apparently customizable. From the Team Blog:
"We knew that using a ribbon for Explorer would likely be met with skepticism by a set of power-users (like me), but there are clear benefits in ways that the ribbon:
-Exposes hidden features that they already use but which require third party add-ons to use in the Explorer UI today.
-Provides keyboard shortcuts for every command in the ribbon, something many people have been asking for.
-Provides UI customization with the quick access toolbar, taking us back to a customization level that is basically equivalent to Windows XP."
It will depend a lot on the specific product. For example, I'm sure that Eclipse very rarely runs with fully default settings. Consumer products will run in more of a default state, until they get very important to people's lives (I've noticed an increasing awareness and ability with Facebook privacy settings among non-technical friends in the last year).
"We knew that using a ribbon for Explorer would likely be met with skepticism by a set of power-users (like me), but there are clear benefits in ways that the ribbon:
-Exposes hidden features that they already use but which require third party add-ons to use in the Explorer UI today.
-Provides keyboard shortcuts for every command in the ribbon, something many people have been asking for.
-Provides UI customization with the quick access toolbar, taking us back to a customization level that is basically equivalent to Windows XP."