Ever wonder why Firefox makes you wait three seconds before you can install an extension or other add-on? I have, and apparently Jesse Ruderman figured it out.
Apparently, there's a tendency for people to click "okay" or "install" or "yes" as fast as possible without reading any warning or notice dialogs when they think they know what they are doing. This can be dangerous if a site is trying to trick you into doing something that you wouldn't have otherwise done. There are also sites that will take advantage of the "y = yes" keyboard shortcuts that are common in a lot of applications and trick you with a 'captcha' like the one in his post.
I'm a geek, but it answers one of those nagging questions that I probably wouldn't have figured out on my own.