I have upgraded from Ubuntu 13.04 to 13.10 and it now constantly duplicates my key presses when I am in a browser, HUD or libreoffice. So if I type "ubuntu" it types "uubbuunnttuu". When I press backspace it eliminates two chars at once. The only exception is terminal. It behaves as usual. The problem is very frustrating, I can't get to work with it, please halp me.
Maybe your keyboard settings got a little out of whack. Try this: