I've gotten paranoid reactions even from people in our wedding pictures at the Laughing Bear site. One couple demanded I not use their last name. They think millions of people around the world are going to be looking at them, when in fact only 100 or so a month drop in. Questions of copyrighting web sites and the material on them often comes up on the PMA e-mail list. A web site is a published work, and should be protected, however the whole thing is so new the laws haven't been put to the test.
People do copy things without giving credit, but the same can happen with books.
You've got to balance the risk against the rewards. I can see a major change coming in the world wide web. People I work with and my relatives are beginning to use the internet to hunt down long lost family members, share photos, and keep in touch with their families. When the majority of people using the internet were teenage computer nerds, the internet was a fad. When grandmothers started setting up web sites for the family album, that was the beginning of an institution.