I've been reading stories on this site for a bit now, so I decided to share the only experience I've had, even though it's from a few years ago so the details are a bit fuzzy.
I was at my grandparents' house in Pennsylvania, not far from Philadelphia, and my sister and friend decided to use a Ouija board up in my mother and aunt's old bedroom, where my grandfather's old things were kept after he died (about a year beforehand). I fought them on it for about five minutes, but eventually gave up, being the only one with any belief in the paranormal, and ouija boards scared the living daylights out of me.
Nothing happened and first and we were quickly bored and decided to watch television. While we were doing so, sitting a good 5 feet away from the ouija board, the pointer started moving. We immediately shut the TV off and sat down around the board, too scared to speak. My sister began asking questions to the spirit: who it was, did they know our grandparents, why were they here. Right after she asked why the spirit was there, it began to spell out "for Domenica". We had no idea who "Domenica" was, and became so scared that we threw the ouija board into the closet and ran downstairs.
At dinner, when my grandmother was out of the room, my sister asked my mother who Domenica was. Though most people had only ever known her as "May", it turns out Domenica was my grandmother's name. My sister and I are convinced to this day that the spirit we contacted was my grandfather.
I realize now how lucky we were, considering what sorts of things can happen using ouija boards, and none of us have used on since. After realizing that they could really work, they frighten me even more.