At the Games Developer's Conference GDC 2011, Raph gave a very good (if long) talk. And I especially liked the part where he talked about incomplete information as a game mechanic (the "Strategy guides" bookmark at the link above). He makes fun about the people who say that reading a strategy guide, for example for a World of Warcraft raid, "isn't really cheating. Because it doesn't really tell me how to play the game. I still have to tap the button in my synchronized swimming exercise at the right time." He then points out that incomplete information is an important game mechanic of many games, like Poker or Stratego. Or even Scrabble, where he cites the LA Times about an online Scrabble Cheat-o-Matic site which gets 120,000 page views a day since you can play Scrabble on Facebook.