While visiting a recent photo-club exhibition, I saw watermarking on a vast majority of the printed art works presented. This is really disturbing not only for your eyes but also the concept itself of adding some text on top of your work.
While asking the members of the photo-club, they told me this is recommended practise to "protect" their work. I think "protect" in their view means limiting the distribution of their picture. Indeed, when you look at a picture with a watermark below distracts your view, your mind and then, it's just distracting from seeing the picture. So you tend to move away from the watermarked pictures and concentrate on the pictures without watermark. At the end, I was more interested in the work of someone having an interesting set of negative-space pictures without any distracting marks or tags.
Then one member of the photo-club told me that everyone was really attracted by those minimalist pictures. Indeed the pictures were nice and well done but I think the factor of water-marks for the other pictures is not to under estimate. People focus on the pictures who attract their eyes (and their brain), this is very human. If you add some complementary factors, your work is less accessible and by so you'll get less potential viewers. Especially adding water-marking on art works in an exhibition doesn't make sense.
For watermarked images on Internet, it's exactly the same. People tend to move away from the watermarked images. If they search for an image or a topic in an image search engine, they will see a whole list of pictures. They won't select/click on the ones having a clear message for them and not the ones with random text on top of the images.
If you are afraid of someone use or reuse your work, the best is to publish your work. The more your work is known and attributed to you, the more you protect your work. The watermarking basically does the opposite, limiting the distribution and especially the possibility to reinforce the attribution to your work. The more viewers you have, the more potential attributions you might have.
My work is freely licensed under the CC-BY-SA license (or even the GNU GPL license) and the non-visible watermarking is in the meta-data (EXIF).
I don't like watermarks, what about you?