I've found quite a few of my images on various sites. Usually Myspace type stuff but one that bothered me was another forum I'm on all the time and a woman used one of my images as her Avatar. I called her out on it and she just ignored me like she knew nothing about what i was talking about.
I used to watermark my images right across the middle, but I've come to the conclusion that if someone wants your work, they will go to great lengths to get it. So I figure now I dont consider myself a professional, I consider myself a Charity Photographer. I take pictures and give them away