Once I thought of a video game idea that was pretty much the same as Battlefield 1942. It was about 2 years ago, and my friend and I were exchanging ideas for video games (yes, we're sad people), and I told him my idea for an online FPS where you fought battles with (usually) huge numbers of people, used vehicles on land, sea, and air, and fought for territory. The only big differences in my idea was that it was set in the Halo universe, and that I didn't think of a class system. Imagine how spooked I was when I heard that a game, almost exactly like this, was being released.
Has anyone had similar experiences?