I once read in a newspaper that the ideal alcohol level is 0.3 (which corresponds to one beer and one drink). This loosens up your body and removes "anxiety", making you feel relaxed and comfortable.
Personally, I've made a decision to cut down on drinking when I'm going out, chicks are not impressed by drunk guys and slurred/unclear speech will get you shot down faster than you can down a shot*. Also, too much alcohol can affect your abilites in bed. Whisky-dick is not a cool thing
* This of course doesn't apply if you've already gamed a chick and gotten into the comfort-zone. Drinking / getting drunk together is fine.