Well there isn't much you CAN do. Oh sure you can bitch and moan on the forums and to your friends. It might get you somewhere but chances are you will look like an idiot. You just have to sit back and let it go.
However, I think this is one of the factors that started the "get to market" first attitude of many magicians today. They are afraid they will be left behind or ripped off so to protect their ideas they are forced to sell it and therefore devalue it a bit. It's a fine line a magic creator walks. Mind you if they are a truly creative person losing one idea to someone else is not that big a deal because by the time everyone is catching up they are still 3 steps ahead.
It can be a frustrating ho' however.