When you type a password into a web form, it's usually starred out, so that people who are sitting beside you can't see what your password is. Obviously, given that typing is hard, that means we can't see when we've made a mistake. Not such a big deal when logging in (you just get an error message), but if you're creating an account somewhere it's a problem.
The standard solution is to provide two starred-out boxes - it's unlikely that someone would accidentally mistype something twice. If both boxes are the same you can assume the user really meant what they entered.
All well and good. A straightforward fix for a simple problem.
However. When entering your email address in an account creation form, it generally isn't starred out - you can see what you're typing. If you type your email address wrong you can correct it.
WHY THEN DO PEOPLE INSIST ON HAVING A CONFIRMATION BOX?
It makes me so angry.
I don't really get out much.