Here's Charlie Petit on a writers' bulletin board on the subject of Poor Man's Copyright. He did a much longer and more detailed rant in Speculations, a zine for sf writers, but I will be good and respect his copyright. I'll see if I can dig out a couple of other links - I think he may have covered this in his blog as well. It is well worth checking out his website, especially the section on copyright - much information that people here will find useful.
Just a comment on the so-called "Poor Man's Copyright":
It's useless. And has been since 1909. That includes the ad that is currently running in writing magazines for the "service."
All of this nonsense comes from evidence law, not intellectual property law, as it was described in some really bad "inventors' guides" in the 1930s and 1940s. Until the reform of the Patent Act in the 1950s, it was very difficult (or impossible) to get regularly kept records, such as laboratory notebooks, admitted at the Patent Office to prove date of conception, date of reduction to practice, or the on-sale bar date. The Patent Act's reforms were later extended by implication (that is, not very clearly!) into the Federal Rules of Evidence. It is now routine to admit regularly kept business records, such as one's submission log, into evidence for the truth of the matters stated on those records. In any event, the copyright
In any event, there's another reason that "poor man's copyright" isn't helpful: One cannot sue on a copyright in the US without registration. The certificate of registration, on its face, provides all of the prima facie proof of conception (etc.) needed for a copyright claim. If things are getting more complex than that, the poor man's copyright won't be helpful in any event.
So, then, here's the bottom line:
Keep regular business records of completion and submission of works. In particular, keep copies of your cover letters, and preferably a CD-ROM that you've burned with the completed work as soon as you complete it. These business records will be admissible to show when you made a protectable expression.
Register your copyrights for material that is significantly at risk of infringement. (The details of THAT are not for this board!)
Ignore anything in between, especially if a third party tries to claim that you really, really need to pay for their service in order to protect your rights.
If you're dealing with Hollywood (TV or film), make sure you follow all of the "idea protection" rules... none of which are followed by a "poor man's copyright".
C.E. Petit, Esq.www.authorslawyer.com-- Jules Jones