Per copyright.gov:
COPYRIGHT REGISTRATION
In general, copyright registration is a legal formality intended to make a public record of the basic facts of a particular copyright. However, registration is not a condition of copyright protection. Even though registration is not a requirement for protection, the copyright law provides several inducements or advantages to encourage copyright owners to make registration. Among these advantages are the following:
Registration establishes a public record of the copyright claim.
Before an infringement suit may be filed in court, registration is necessary for works of U. S. origin.
If made before or within 5 years of publication, registration will establish prima facie evidence in court of the validity of the copyright and of the facts stated in the certificate.
If registration is made within 3 months after publication of the work or prior to an infringement of the work, statutory damages and attorney's fees will be available to the copyright owner in court actions .Otherwise, only an award of actual damages and profits is available to the copyright owner.
Registration allows the owner of the copyright to record the registration with the U. S. Customs Service for protection against the importation of infringing copies. For additional information, request Publication No. 563 "How to Protect Your Intellectual Property Right," from: U.S. Customs Service, P.O. Box 7404, Washington, D.C. 20044. See the U.S. Customs Service Website at
www.customs.gov for online publications.
I'm not a lawyer, but based on what the copyright laws in the US say, you're not even going to get your case into court if you DIDN'T register...
