As far as I can tell, watermarks are for professional photographers. I do have a PRO account on Flickr, but I still do not qualify:)
Lightroom can add watermarks to photos. Looks like an easy thing to do, but I have never used it. Side RANT, you can easily add a watermark, but adding simple text to a photo is difficult!
I do add a lot of metadata to my photos, but of course metadata can be easily removed.
I publish all my photos with a Creative Commons copyright, share and share alike.
I shoot in RAW and publish in JPEG.
