Now, I'm not sure if this means this is the day to buy a microwave oven or cook something in a microwave oven. I'll assume the former (though maybe this is a good day to finally replace the one you've been using for 15 years).
There are actually several books about microwaving oven cooking: Microwave Gourmet by Barbara Kafka, A Man, A Can, A Microwave, by David Joachim and Men's Health, and perhaps the first (or at least one of the first) books on microwave cooking, Richard Deacon's Microwave Oven Cookwave. Yup, the same Richard Deacon who played Mel Cooley on The Dick Van Dyke Show. He also has one titled Richard Deacon's Microwave Cookery. Not sure if it's the same book or not.