I was pretty messed up already during the time I first used one in my early to mid teens, but nothing really bad ever happened to me or anyone I cared about during that time and I used it by myself. This was during middle school, at the heels of my parent's divorce, and when I was an avid reader of horror and the brunt of cruel remarks in school every day. I never channeled any hostile spirits that said spooky things or made the board fly or glass explode. Perhaps remarkable, because it was all around a dark period of my life with a lot of negativity. No drugs, though, fortunately.
After my classmates and I matured and I entered high school, that phase of my life ended. I think what helped the most was a prayer before the session, asking for protection and for no harm to come to me while I experimented with this. I also pretty much convinced myself, especially after reading something about automatic writing, that I was probably moving the planchette by myself.
Admittedly, going it at alone may have been a big mistake but solitude is something I had always been used to. I must have been fortunate (and wise to have protected myself beforehand), but I payed for it with a further disconnecting with reality during that period of my life. Mileage may vary, and I agree that it's very important to take protective measures as well as be careful what you ask and who you conjure up. It probably should never have been in the "toys" section back then. A couple years later I ended up throwing it away with no one knowing that I did, and with no coaxing from anyone except for my own feeling that it was the right thing to do to move on and improve my spiritual/mental health.
I'd be interested to know what ever became of what you originally posted about, shotthebreeze.