I am in the process of submitting my thesis online. I think most of the people here are familiar with ProQuest. One of the option you have is to have them register the copyright to your thesis with the US Copyright Office (in your name).
From my point of view, a thesis should not be copyrighted simply because I think of it as an extended paper. I will gladly let people use my work and cite me appropriately.
Having seen that option though, I am wondering if there is any reason to register the copyright to a thesis.