I really think that a watermark detracts from a photo. I get the point about protecting your work, of course, but the damage that it does to the art... (and I've never been very shy about voicing my opinions).
Also, most of the watermarks that I see would be pretty easy to crop out if theft were the point.
If I were going to watermark my stuff, I think I'd look at a more steganographic solution. There are several out there.
