The DMCA Contact posting, and the link to it in the header, are there to make sure that if someone unknowingly infringes copyright in a comment, that the copyright owner is obligated to contact me before filing suit. This could be done by accident, by malice, or by employees of a firm looking for a chance to sue. It doesn't do any good for anything that I intentionally post here, of course. But it does provide some protection for the actions of a commenter.
If your blog allows comments, you darn well better have a DMCA Contact information link somewhere on every page of your blog.
UPDATE: It appears that you need to register with the Copyright Office for this to work--which is $105. Nope. I'm just going to moderate all comments. It's a pain--but the alternative is turning off comments.