Heh. Only twice? ;-) You've almost certainly missed some of the games.

I took a seminar with Hofstadter in the early 80's about the book. I thought I'd read it thoroughly, and I was stunned at how much I'd missed.

I don't have my copy with me, but a couple I remember:

• A reference in the bibliography to "Copper, Silver, Gold: An Indestructible Metallic Alloy" by Gebstadter, Egbert B. The book is described as "a turgid, confused mess" (something like that), which is an actual quote from one of the first reviews of GEB (pre-Pulitzer, of course).
• A lot of people miss the second level of "Contracrostipunctus". If you line up the acrostic, it reads:

  Hofstadter's
  Contracrostipunctus
  Acrostically
  Backwards
  Spells
  'J. S. Bach'

  And it does, down to the punctuation!

For more fun, read Le Ton Beau de Marot for some of what they went through to translate GEB into other languages.