There is a peel-off problem though. In many N9 users.

Off course wearing a case helps greatly.
The bad thing with case is that the phone feels somewhat larger and the swipe gestures feel less natural.
But worst of all ... the dirt somehow goes in the case and dust or dirt can sometimes scratch the back of the N9.

check the images in the forst post of this thread:
http://talk.maemo.org/showthread.php?t=82755