There is liquor available for purchase on-board, and since US taxes don't apply, it is much less expensive than in the States. If you want to drink it on-board, there is a $10 corkage fee (which still leaves most of the bottles less expensive than in the States).
I hope that it is true that you can buy it on board. I have been reading on many different cruise sites conflicting stories about this topic. Some say that if you buy it on board you have to wait until the end of the cruise before they release it to you, others say you just pay the $10.00 fee, and can take it back to your cabin. I don't know why people would go through the trouble of smuggling their own liquor on board, if they can just purchase it on the ship. Makes no sense.
I bought liquor on the Serenade of the Seas, and it cost $10 to take it back to the room. However, before our last day at sea the salesperson said they weren't charging the $10. So, I bought a bottle, and we drank it all day long on our last day at sea. Unless you can find a way to bring alcohol that you buy during the cruise onto the ship, it is not worth smuggling it from home....at least in my opinion. :-)
They deliver the liquour at the end of your cruise. You are supposed to hand it over when u buy in port also. They have tables set up when u get back on ship. They give you a reciept and you get it on the last evening.