I've recently had issues with a photograph being used in an unauthorised commercial fashion. As my photography has improved, I've had to look at my images in a different light. I no longer publish them on websites such as TMA and have pulled a number off the net that I'd already published.
Watermarking is another obstacle if I'm going to post photos, and one that just makes the whole process more time-consuming and less likely to take place. Embedding automatic watermarking software on a site such as this should be quite easy and would be a step in the right direction, IMHO. I regret having to remove photos and would like to be able to contribute again.
The other option would be to use some form of flash software to make the images less vulnerable to the casual right-click copier. This is again relatively simple, but it would be a fairly large job to build it into an established site such as TMA. I use Simple Viewer on my own site, which allows me to post my images in the knowledge that they're unlikely to be nicked.
Posting stuff on the net is always a bit of a conflict for me. I have no objection to my images being used casually for non-commercial ends, but the more people who copy and reproduce them, the greater chance that commercial theft will take place. It's a tough one.