On the Newsletter (signup) page, I entered Heir Apparent into the textbox. The site started doing weird things and the music changed. A kind of handwriting started to appear above the textbox and it said "Can you read this?" I said "yes" and then it said something like "It's me, Persephone." Then it asked me to enter the password, so I entered the same thing. The next message was "Call the call center in the TV ad section." Then the site went back to normal. I'm looking at the TV ad section now, trying to figure it out.
EDIT: It turns out that any name can be entered and you get the same result, so I'm not exactly sure what Heir Apparent is for.
EDIT: Well, I figured out where Heir Apparent goes, but this site is full of easter eggs. Go to 4815162342.com if you really want to find everything and see what others have figured out. It's way too much to post about here.