I think they're legitimate, make it at least a little harder to rip your photos off. I know we're putting them up here, but shouldn't be too easy to others to steal them and say they're theirs.
As long as the watermarks arn't huge and run through the center of the photo I think they're legit. Even painters sign their names at the bottom of a painting, sometimes the date.
http://365project.org/discuss/tips-n-tricks/2798/create-a-custom-brush-for-watermarks
http://365project.org/discuss/general/3495/watermarks
http://365project.org/discuss/tips-n-tricks/4233/watermark
http://365project.org/discuss/general/2782/watermarks-how-do-i-in-photoshop-elements-8
http://365project.org/discuss/general/1279/help-i-need-a-watermark
thanks