We were in the Galápagos last Sept.--the time of the choppiest seas. Among our group of 16, about 2/3s used some kind of motion sickness remedy. By far, the majority were using the scopolamine patch mentioned in #4's response. My husband is a sailor, so we figured he'd be fine; I had never been on more than a day trip, so we brought the patches along for me in case I had a problem. Ironically, it was my husband who was affected and I was fine. (I think it had to do with being inside. Any time he was on deck and could see the horizon, he was fine.) The patches worked great for everyone who was using them; however, at least with our drug coverage, they were a bit expensive--but well worth it, in my opinion.
So as a cautionary tale for any who think they don't need to bring something--you might think again. It's a simple thing to bring along some treatment; and why risk ruining the trip because of something that is so easily preventable? One note of caution--the patches we had were designed to be replaced every 3 days. However, my husband accidentally washed a couple of them off in the shower. Luckily, we had spares, so there wasn't a problem. But if you're taking patches, see if you can bring a few spares.
Tina
trip report at http://galapagos2009.wordpress.com/