I have instantly left every website that uses them.

My theory is that it is an indicator of low-quality content ("we have to get their info before they figure out that we aren't worth it!!!"), and respond accordingly.

I can't say that my life is worse off because of it.

Every so often when I encounter one of them and am a bit bored, I enter a nonsense email address. Usually, though, I close the browser tab with the site spawning one of those boxes, often never to return.