I suspect, but don't know, that watermarking is really only going to be effective in hindering the casual but not professional user of pinched images. I would imagine that somebody who doesn't even have the mechanism for cropping available in his computer will not be going to knock off a pic that shows a clear watermark - can't be that stupid...?
As I'm currently in the struggle of putting together a website, I feel the conflicting temptations between going for large enough images to show off, not putting on any scribbles of ownership on the images themselves, or staying with small sizes and thus probably spoiling the thing for myself. There is the school of thought that says anything on the web will probably get ripped off, but I hate the thought of being a willing rape. Worse, as almost all the interesting stuff was done on commission, I have worries about old clients or models getting their knickers in a twist if material appears in illegal reproductions. Sod and his Laws, of course.
Perhaps that's why, apart from lack of tech savvy, I still have nothing posted up beyond a white page!