"Adults at least 21 years of age who are not residents of the United States may bring in, free of duty and internal revenue tax, not more than one liter of alcoholic beverages beer, wine, liquor for personal use. Quantities above one liter are subject to duty and internal revenue tax and all must be declared.
DUTY AND TAX RATES SAMPLES (Approximate):
Beer - 16 cents per liter
Still Wine - 36 cents per liter
80 Proof Scotch - $2.89 per liter
In addition to U.S. Federal laws, the traveler must also meet state alcoholic beverage laws which may be more restrictive if the state in which you arrive permits less liquor than you have legally brought into the United States, that State's laws apply to your importation of alcoholic beverages.
The shipment of alcoholic beverages by mail is prohibited by United States postal laws."
I don't understand why Americans get so weird about paying duties, they generally aren't much. When I returned from my tour in Antigua, TWA, I brought two cases of rum along. The duty back then was 40 cents a bottle and I only paid 80 cents each at the distillery.
For beer, the duty is probably far less than the shipping cost would be and you don't run the risk of losing it or having it damaged or mishandled.