This membership gives players access to "exclusive items," including an early playable demo of Duke Nukem Forever before it's public release.
2K did not say when the demo would be available, only confirming it'll be out "prior to the retail launch of the game," which is still marked for calendar year 2011.
Borderlands Game of the Year Edition ships on October 12 for Xbox 360, PlayStation 3, and PC. The pack includes all four downloadable add-ons: The Zombie Island or Dr. Ned, Mad Moxxi's Underdome Riot, The Secret Armory of General Knoxx, and Claptrap's New Robot Revolution.