Go to the Special Features page and as soon as you get there press "Right" on your remote control, a guitar string will highlight, press "Enter" and you will be taken to a new menu with some special behind the scenes footage (with optional commentary by Christopher Guest and Eugene Levy no less) and a chance to read some of the fake newspaper articles up close (My personal favorite is the one about the TV show starring Fred Willard's character getting cancelled)
This easter egg was generously submitted/corrected by Davart
On the special features screen, when you're at the top of the list of features, click to the right instead of down--the guitar or banjo string to the right will be highlighted. Click enter and you will find two hidden extra features, including a silly shoot of one of the scenes in which the characters of Lars and Johnathan are played by two of the producers ("Johnathan" behind a popsicle-stick mask of Bob Balaban).
This easter egg was generously submitted/corrected by SirDonk