I've been searching the forums for a post on this topic and haven't been able to find anything so I thought I'd add this topic for comment.
I just got back from a Holland America Line cruise on the Oosterdam with stops in San Juan, PR and Amber Cove, DR. A few days before I boarded, I was looking through the info for "already booked" and found that I could purchase a bottle of alcohol with mixers for in-room consumption through room service. I could have also ordered through the website to have it in my stateroom when I arrived on the ship.
I ordered a bottle of Jameson Irish Whiskey by dialing 92 and when the bottle was delivered it was a full liter and not a 750ml as I expected. The price including gratuity was only $56 which is a steal considering mixed drinks for a 1.5 ounce pour were in the $10 range with gratuity. This was a no brainer as far as cost and the small inconvenience of walking down to the room to pour a drink was well worth it. Truthfully, I usually took my drinks up on deck or anywhere else on the ship that I wanted to with no questions from staff or crew.
It was also a great thing to have in the room for small get-togethers with friends for shots before attending entertainment events.