Type any of these to get some weird hidden objects:
All your base are belong to us
Om nom nom nom
Over nine thousand
I see what you did there
Do not want
Whenever in game or at the Start menu: spawn a Teleporter and 'ride' it.
This could take you to a few different places, but more common than all it will take you to 5thCell Studios. There you can walk amongst all the Developers of the game.
During the title screen type in SCRIBBLENAUT and you will see the beta version of Maxwell.... He doesn't do much.