Kendo - 3:16 am on Apr 25, 2013 (gmt 0)
you should take a look at the official statement from the Copyright Office
This may apply to content within the US, but even then it won't be reliable. For example if I can prove originality and date of creation then nothing registered anywhere else will help you at all.
Likewise with patents... so what if you registered a patent based on my product?