Stephen, i have never read anything written about the effectiveness/ineffectiveness of Ouija boards but i have had an experience with one that turned up one piece of info that was verified.
Many years ago i was involved in a bit of Psychic questing helped along with the board. One bit of info that was gleaned regarded a wood in our area that none of us had ever heard of, but part of the information gave us an aproximate location which we knew of. One of my freinds mothers worked at the local council planning office and he managed to look at the old maps of the area and came across one that was about 100 years or so old that actually named the wood on it in the area that we knew. As far as i know the name of the wood was never printed on any newer maps.
Also once at a supposed haunted location the board was brought out and the message beware the three bells or something like that was spelled out, i must admit i was asleep at the time of this board being done but at aprox 3am all the burglar alarms in the building went off, i've never been so rudly awoken...
Best Regards
Lee.