It would be very valuable to developers writing Web applications (as opposed to simple pages or fill-in forms) to have the ability to theme a button control with the "default" (glowy blue in Mac OS X) appearance to indicate that pressing return will activate that button. Although the implementation details are sketchy if the button is set up as the submit button for a form (if there are multiple forms on the page, should both submit buttons be default at once? Only the one whose associated form has keyboard focus? etc) but this should definitely be available as an attribute (perhaps accesskey="↩") or a CSS value ("-webkit-appearance: button-default") for developers who wish to manually associate the button with a return key press in a JavaScript event handler or similar.
*** This bug has been marked as a duplicate of 16645 ***