I have heard that chocolate is good for you. Is this true???

Chocolate is rich in plant polyphenols, and especially in a subclass of polyphenols called flavonoids. These substances are also found in other foods such as bran, apples, pears, red wine, grapefruit, and strawberries, but in Western countries cocoa products contribute a large proportion of polyphenol intake. These substances have been reported to improve vascular function, dilate blood vessels, and reduce the likelihood of clots forming where we really don't want them, such as in the arteries of the heart and brain. The beneficial effects are seen only with dark chocolate, which has a lot of polyphenols, and not in white chocolate.
But it is very important to understand that chocolate also has a lot of calories. If you 

consume hundreds of calories of chocolate every day the beneficial effect will be more than offset by all of the problems related to overweight, such as high blood pressure, high cholesterol, and diabetes.