I wanted to subclass UINavigationBar (to set a custom background image & text color) and use that for all the navigation bars in my app. Looking at the API docs for UINaviga
I dunno if you got this figured out. But for others that might have this problem...
What you need to do is to specify the class in your XIB to your class name (in this case MyNavigationBar.
Check session 123 in WWDC 2011.