in reply to The most useless key on my keyboard is:

There's a key in the top-left, next to the 1, that has three symbols on it, ` and |, and I don't know how to make it procude a |. I don't use ` and as to what a is, I have no idea. The only time I've ever pressed it is to see what it does.
UK keyboard
Oh, hang on, I do use ` occasionally if I'm using a unix shell, so maybe it is useful, but not to a Windows-type like me.