I watermark photos just because I want one little annoying thing to hopefully keep idiots from posting them in other forums claiming they took the photos. I figure by making them crop the photo, and have to re-host it, it just makes them think "eh, too much effort" and it won't happen. I am by no means a professional, but I have been paid for my photography before. So I guess that makes me and advanced amateur and money making hobbyist, and it makes the watermarks seem somewhat valid.