Myth: Decaffeinated coffee & tea is totally caffeine-free. Truth: Not true! Even decaffeinated coffee and tea still has a small amount of caffeine. The decaffination porcess removes about 98% of the caffine, but their is still some there. It still leaves 5mg - 10mg of caffeine or so per cup.
Myth: Caffeine consumption can decrease bone density. Truth: Researchers have found no direct link between low bone density and high caffeine intake. Studies done at the Mayo clinic have found that even though caffeine intake marginally increases urinary calcium excretion, caffeine was not an important risk factor for osteoporosis.
Myth: Coffee will help a hangover. Truth: You wish. Caffine, be it in coffee or other things, won't help someone "sober up". The 'sobering' effect is really just a normal caffeine hit taking effect.