I don't know when it was introduced, but the sideways scrolling history navigation thing has caused me to lose form input several times now. I use a trackpoint, so it's really easy to scroll sideways instead of up/down accidentally (middle button + trackpoint). I guess that's a very niche problem, but I've lost a lot more input that way than via backspace.

At least Chrome shows a helpful "Use Alt+Left to go back" message when mashing the backspace key and expecting it to go back.