Bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease: how safe is eating beef?

Cases of bovine spongiform encephalopathy (BSE, mad cow disease) have been found in North American cattle. Its human counterpart, called variant Creutzfeldt-Jakob disease (variant CJD), is rare but seems to be linked to eating diseased beef. Many questions remain about these diseases, such as why young people seem at greater risk of variant CJD. Also, are some people more genetically at risk for acquiring variant CJD than others?