I've done a lot of research on this for work as well as my own personal edification. I have completely given up alcohol, except on special occasions for now, mostly because alcohol has no real health benefits and I just don't want to do it anymore.
That aside, there have been a number of studies that show that consuming more than 2-3 drinks per week actually does restrict nutrient absorption, which will lead to loss of lean muscle mass.
Alcohol is also a natural depressant and will begin to drag on your metabolism and in some cases your mood. Mood state can certainly affect both quality and quantity of workouts.
As with anything nutrition related, different people respond in different ways to things.