An online banking site which I use, has a "feature" which disallows a user from pressing Enter to submit a login form. For example, if you have typed your username in the Username field, pressing Enter will show a message "Please click Login to login".
Most users would follow by using the mouse to point and click. However it is actually possible to just press Tab to move the focus to the button, and press Space to submit the form.
Do you think "preventing form submit by pressing Enter" or "asking user to use the mouse" is a case of security by obscurity? They aren't using on-screen keyboards though which I believe are supposed to circumvent keyloggers.
What sort of attack/threat would this measure be likely to circumvent?