The XP Control Panel is a case in point: almost everyone switches to Classic view since this is what they are used to. I even switch XP Playskool theme to the Windows 2000 Classic theme and know many who do the same. Terms like "slick", "sharp" and "pretty" are irrelevant when they cause users to be confused by a new interface and revert back to a less pretty but familiar interface.
It really doesn't matter what interface we eventually go with because people are going to have to learn it. That it takes lessons from the current GUI 'norms' (assuming such exist) is good. What does matter is that we decide on rules and guidelines for it. Then we publish those rules and guidelines for contrib.
That was my point : familiarity. No matter what we use, it is a question of learning it. All we need to do is make it consistent, and users will have to learn it.