The chess blogs are buzzing with the story about Ukrainian Andrey Slyusarchuk beating Rybka 4 in a blindfold match. Despite the match being televised, the general consensus from within the chess community is it is some sort of trick. The fact that Slyusarchuk does not have a strong chess playing background, and is currently declining any other matches against humans or programs, lends weight to this belief. The main point of discussion is how he did it.
Although I haven't looked too far into there is at least one way it could be accomplished. Assuming you can set Rybka up to play 'repeatable' chess (turn off any randomness in the opening book and move selection, turn off pondering, and set it to a fixed search depth), you play it against another strong program until Rybka loses. Then it is a matter of memorising the game (or in this case two games), and simply repeating the moves, after suitable thinking time, face pulling etc
Now I'm not saying that this is how they did it, but if I was trying to pull something like this off, it would be how I would do it.
Anyway, both Chessbase and Chessvibes are on the case.