Everyone seems to ignore the following, but its generally illegal to ship consumer-to-consumer. It varies state-to-state, but I think its technically illegal in all states. Its a felony to go into certain states too. So don't get caught. We really need a law that explicitly allows homebrews to be sent for competition, etc.
I work for a wine company and its an enormous pain to get all the permits in order, post bonds, pay taxes, keep track of quantities shipped to each person, etc. Its worse for beer than wine in my experience.
The pesky 21st amendment has a clause that while making alcohol legal again after prohibition, it lets the individual states control interstate commerce. This is different than most products.