An interesting article about copyleft in New Scientist. It mainly talks about the possible application of copyleft to information other than programs. Is it applicable? I think so.
Copyright is a good enough idea, though it has been slowly distorted over the years so that its advantages to the public are now much smaller than they used to be. (That sort of degeneration is inevitable for all State creations, not just copyright.) One of the great advantages of copyleft (and other forms of free information, including BSD-style licenses and even public domain), is that it serves as competition to copyrighted stuff. Such competition is increasingly necessary as copyright owning rent-seekers manipulate public policy in their self-interest.