Thanks for your thoughts. Yes, I do intend to ask permission as a matter of courtesy and ethics, and list all sources in the bibliography. But it is also important to understand that legal considerations don't require it.
My knowledge of copyright law and intellectual property is from music and books. In these cases (and presumably this would work in magic as well, if the copyrighted work is merely the book itself), you cannot simply make "small variations," otherwise you would be making a derivative work and infringing upon the copyright. I think what Richard was saying was that, for instance, Guy Hollingworth's riffle shuffle and triumph handling method itself are not protected by copyright law (for better or worse), yet if I basically quote the specific description of it already published in Drawing Room Deceptions, I would be breaking copyright law.
It is an interesting issue, because it would seem that the more important "creation" of magicians would be the effect or technique that they invented, and not the mere book or article that describes it. A songwriter gets paid a mechanical even if somebody else records their own "handling" of the song, making changes, etc. Once a song has been recorded and published, anybody else can record it without permission, as long as they pay a compulsory mechanical fee to use it. If magicians were protected by copyright law in the same way, then they would get paid a fee if somebody else used their effect.
After all, when an inventor invents something and that invention is protected by patent laws, it's the invention itself that is protected, and not merely the blueprints that it was written on. It doesn't seem fair to me not to extend copyright or patent protection to magical inventions. Has anybody ever tried to patent an invention in magic, or is it just cost prohibitive?
I suppose there is a plus and a minus to all of this. The minus is, of course, that inventors of magical effects do not have their rightful intellectual property protected by copyright or patent laws, and do not profit equitably when they invent something of sufficient value that it would be used in other works. But on the other hand, it's good for the field in that information gets distributed more freely.
This begs another question for some of the long-time pros: has there ever been a movement or lobbying effort to get the copyright laws changed to protect the works of magicians?