there are many inter-individual differences in susceptibility to alcohol-related damage. Often there is a family history of alcoholism and developing liver damage. depends upon ethnicity, body habitus, gender, etc.
See: http://www.liverfoundation.org/education/info/alcohol/ for discussion of alcohol consumption and effects on the liver. It has a section on "Safe" consumption levels.
Research shows that genetic factors may determine those at increased risk of developing liver disease when certain genes trigger a strong immune reaction in response to alcohol which damages the liver.
A doctor from University of Newcastle upon Tyne (United Kingdom), presented his findings at the American Association for the Study of Liver Diseases (AASLD) 2000 Annual Meeting. His studies may indicate why some heavy drinkers develop liver problems, while others do not.
One in five heavy drinkers develop liver damage, and he believes his research will help identify people at high risk of developing alcohol liver disease and develop treatment for those at risk. (http://alcoholism.about.com/cs/liver/a/aa001116a.htm)