Semi tangentially, the 'backspace = go back' shortcut has accidentally deleted countless posts and emails of mine (and I'm sure many other people's). I really think that shortcut needs to go away.
Not sure about the other browsers, but this is mostly a solved issue in Firefox: it has grown clever enough to remember the contents of a text box even after going back, closing the tab (reopen it with ctrl+maj+t), or even quitting Firefox.