I was also raised with the notion that Ouija Boards were of the devil, being that I come from a very religious family. My dad has told me several times about some kids from his high school who were killed when their car crashed and got wrapped around a telephone pole after playing the Ouija.
As an adult, I played the Ouija once. It was very interesting, as I played with a group of kids who were rather into the occult and played so much that they even made their own boards b/c their real one was so worn out and eventually taken so many places it fell apart. When I played, it was obvious that the indicator was moving on its own, because there's really know force applied by the players, you just lightly rest your finger(s) on it. Then, I asked it what my SSN was, and it got the first 3 numbers right but then got confused, but it kept going back to 6, which actually the last 6 digits of my ssn is a 6-then a #, 6 then a #, 6 then a number. So it knew the 6 pattern. I have no idea if that means anything lol. Nothing scary happened, although I was scared shitless for the week afterward that something bad would happen.
Ultimately though, as much as I believe in spirits, I have no way of concluding whether or not it is real spirits or the devil. I just don't know, because even if you ask convincing questions that only the spirit themselves would know, couldn't satan recreate the answers?
Not to mention that I and MANY members of my family have had evil spirits manifest themselves to us, and I fully believe that demonic entities exist, so I don't think it's entirely impossible that the Ouija board could be a participant.