I had a friend with a ouija board when I was a kid. The board never worked for me if I was alone, it only worked for her.
I did try some experiments, though. I had her close her eyes, and it still came out with real words and answers. I also had her lay down so her head was almost even with the board- the answers again still made sense.
Of course, she may have been peeking when I wasn't looking.
When I was visiting her, we did have an incident where the planchette moved. We'd turned our backs to it, and then got up to get pizza, and I noticed it wasn't where we'd left it (I can't remember how I could tell, though, I think it might have been on the floor when we'd left it on the board.) Again, it's possible she moved it when I wasn't looking, but I don't think she did.
I've wanted to get another board, but my husband won't let me. I saw this beautiful slate board on ebay last year sometime, but he refuses to let me bring one into the house. He alternates between saying they're bunk, and between saying that they often invite things in that you don't want. I could sneak one in, but I'd rather not, so I just have to live vicariously through other people's experiences.
Personally, I see the ouija as a doorway that can be opened or closed, and abusing it can lead to bad things. Whether or not ghosts actually speak through it, though, I can't say. It could be tulpas, or subconscious control, etc, but without being able to use one, I can't make my mind up firmly one way or the other.