The biggest thing has gotta be backslash...if you spend ANY amoung of time in a DOS/Windows command line, you need that key to be where you expect it to be, or hammering out file paths takes way longer than necessary.
Making it even worse, if you go for the normal spot and hit Enter instead, you've now got to re-type your entire path (except where the cursor keys can recall the previous command, but this doesn't exist in real DOS).