While mneek is absolutely correct about the value of the original Joy of Cooking as a unique and valuable cultural artifact, for the modern cook who's interested in everyday cooking, the 1997 revised edition is, in my view, the more useful. Let these few simple examples suffice to illustrate my point: While the original edition tells you how to cook whale and make pickled pork, the newest edition describes how to use Thai curry paste and prepare Jamaican jerk marinade. Now which do you think would be more helpful to you?
If I have any questions about basic cooking techniques or about how to handle unusual ingredients like cactus paddles or jicama, I pull out my new Joy. It almost always tells me what I need to know.