Earlier quoted context omitted.
"Ok" for a change (that's described in the body of the dialog's text) is... okay, I suppose. But it's better to mirror the action verb for your confirmation button, because users don't necessarily read the text you present them with. So, instead of this: Delete xyz.jpg? -------------------------- The file 'xyz.jpg' will be permanently deleted. -------------------------- [ OK ] [ Cancel ] You have: Delete xyz.jpg? ---…
Actually "mirror the action verb" surprises/confuses me even more than "OK" "Cancel", since the latter are standard and almost expected, whereas anything other than a positive/negative response feels unexpected. It's like the real-life equivalent of asking someone a yes/no question --- you're expecting a yes/no answer. In fact, I'd say this is even clearer, putting the question at the end and immediately following it…
If the action is to move forward with something or not, I think I prefer the "next"-type button to be on the right, and "cancel" or "back" on the left, probably far left.
But, my thinking does violate the "pick one and be consistent" suggestion. So... I dunno :)