[microtonal]

The average user would not be able to tell the difference between a well-adapting Qt application and a Cocoa application. We have a Qt application for searching treebanks, and when showing it to another Mac user, he replied "nice, you wrote it with Cocoa?".

Twitter's (or the App Store's) deviation from the Mac look and feel, on the other hand is very noticeable. And I am not sure it is proven that we are talking about "extending nicely into a different style of UI". The Twitter UI is plainly confusing (where do you drag this window?) and having the backward/forward buttons next to the window controls is questionable at the very least.

[wtallis]

Did you just show it to the Mac user, or did you let him actually sit down and use it? Qt does a great job of mimicking the look of Cocoa apps, but it doesn't always get the behavior right, and if you're going to behave differently, you ought to warn the user by looking different.