Do you know what's really good for you? In this age of countless miracle cures, it's vital to separate the myths that endanger your health from the medical facts you need. FACT: Unfiltered coffee can clog your arteries. FACT: Donating blood may lower your risk of heart disease. FACT: You don't really need eight glasses of water a day. FACT: Coughing won't help if you're having a heart attack. (But aspirin will!) We've become a nation of cyberchondriacs,...