We ended up booking transport for $20 per person through Jaital round trip from Falmouth to Montego Bay. 30 minutes after we docked, we found the Jaital driver. The four of us along with another couple from Oasis (who had booked separately) went to Mo Bay. It is around a 20 minute ride, very easy. We were dropped at Doctor's Cave Beach and agreed upon a pick up time and place (4 pm, in front of Margaritaville). Remember: stay on ship time and not Jamaica time!
It is $6 per person entrance to Doctor's Cave Beach, and $6 for an umbrella and $6 for a chair (a wooden/canvas deck chair). In hindsight, we didn't really need the umbrellas because there are shaded areas in the back portion of the beach. Clean bathrooms, showers, a deck area for food/drink, and beach service.
I am a jaded, nit picky beach person. This was one of the most beautiful beaches in terms of the water - that I have EVER seen.
We hung out in the crystal clear water for about 3 hours until we got hungry. I wasn't feeling great - the land was rocking a rolling so we walked down the street for a Burger King snack. Doctor's Cave Beach will give you a stamp for entry. We decided we had had enough beach, so we headed down to Margaritaville - about a 5 minutes walk from Doctor's Cave. Margaritaville is a bit pricey, but it was a fun way to spend a couple of hours eating and swimming. They have a water slide on the top deck and it shoots you out to the bay below. The slide is fast and a bit freaky.
Falmouth port is very clean and very RCL World - the same jewelry stores, etc.. that you find in their ports. They are building a Margaritaville - right now there is just a t-shirt shop.
I think our "Jamaica Day" was well worth it, and was easy to plan. We were back in port by 5:00 pm.