Everyone knows that Backspace key is no longer a Back button after Safari 6.0 update. And I want take it back. This is solution:
[Any other ways] replaces the original «cmd-[» shortcut for Back, rendering it useless in text fields. This forum thread has the command to re-enable Backspace without changing your other keys:
defaults write com.apple.Safari com.apple.Safari.ContentPageGroupIdentifier.WebKit2BackspaceKeyNavigationEnabled -bool YES
Useful tip: It also restores shift-delete for going forward. This is a much nicer option, so the original submission should probably be updated to mention it.