I'm interested in some of the legal issues around software licensing, but my question could apply to other copyrightable works too. Most free and open source software is copyrighted but distributed under some license that grants others the right to use it. Other authors instead opt to disclaim copyright entirely and dedicate their work to the public domain. There is some debate about whether this is a good thing to do or not, see for example this article from the open source initiative. In that article and others, I've seen a statement made that "Disclaiming copyright is only possible in some countries."
In what countries can you disclaim copyright? In what countries can you not disclaim copyright? For example, this page seems to say that, under German law, copyright cannot be transferred from one person to another except by inheritance. Does that mean the dedicating a copyrighted work to the public domain is a meaningless statement in Germany?