Watermark or not?

Recently I have discovered that my pictures are used on various blogs, websites and even on flickr without my permission or that they link back or give me credit for the pictures… So I’m somewhat unsure what to do. I don’t like to watermark my photos, I think it disturbs the pictures a bit. But it REALLY disturbs me to see my work being used without me having any benefits or acknowledgment.
Like Shakespeare said: "To watermark or not to watermark? That’s the question."


or not?
[Photos: MayaLee]