When Photoshop asks to replace a file, two boxes are shown, "Cancel" and "Replace."
I use keyboard shortcuts very often to increase workflow speed but when saving out files such as jpgs that will replace old versions, I have to use the mouse to manually click "Replace" rather than simply pressing the Enter key on the keyboard.
If two choices are prompted at anytime in this way, the Enter key should ALWAYS accept the action and the Esc key should ALWAYS cancel the action.