i never press backspace by accident in a form, but i am used to option left arrow moving back one word at a time, not having the whole page go back. The benefit of backspace is that it works like a backspace when you are in a form element. The damn alt left arrow thing makes you go back no matter what you're doing on a page.
Not an answer:
http://ubuntuforums.org/showthread.php?t=1353231