I never use the "Reader" feature in iOS 5's Mobile Safari, and the button for it sits there in the address bar just being a nuisance when I want to see or edit the URL in the address box. How do I turn it off?
I am fairly certain there is no way to disable this feature, short of jailbreaking your device. Even then, I am not aware of any tools to do so. Sorry this isn't the news you were hoping for!