Penn & Teller did a good episode on the Ouija board, having 'professional spirit mediums' using the board (They were so special, they were using a board they custom designed for their use).
Guess what they learned? It's all a bunch of shinannigans! The board couldn't correctly answer anything that none of the individuals didn't already know. They would claim to be talking to someone dead, so the investigators would suggest simple known questions about the person (where they were board, when did they die, etc.), and the mediums would get back wrong answers or it would be 'muddy'. They could only answer things that were subjective and untestable ("He feels sad right now"). They also played a few jests on the participants by blindfolding and rotating the board... and of course, the participants continued to point to positions on the board that they THOUGHT were yes and no (apparently the spirits can't see the board is flipped).
They also described some of the 'mystereous forces' at work. If two people hold an object, and it moves, you know it's the other person. But if three people hold an object and it moves, there is no one person to say 'you're moving it'.. and the object becomes more difficult to keep stationary.
They had some random individuals try it that had never done it before. Roughly half of them felt 'something special was happening', and the other half thought that too many answers were wrong and it was just a game.
My JW mom played with a ouija board when she was a kid, and to this day swears that it told her things nobody else in the room could know (but SHE didn't move it that way), and that night she saw 'shadows' moving around her house, and one of them centered on her and posessed her for a few minutes. Actually, the story gets better every time she tells it. (She was also using drugs at the time, but SWEARS she didn't take drugs that night, and it had NOTHING to do with it.)