I voted for "Did our own thing and enjoyed it". Since Costa Maya was an unscheduled stop for us, we hadn't planned on going there, so we decided to just get off the ship and explore the dock area. Like others have said, the area right at the end of the dock was very cute. A little circular shopping area right on the egde of the water, with a pool and bar, lounge chairs, wading pools (picture fountains in a city, where you can just climb in and play in the water), stores (Diamonds International, Tanzanite International) and shops, and a central area where we saw entertainers, dancers, a mule ride (just like a pony ride, except with a mule, it was cute). As soon as you get off the tram which takes you from the ship to the end of the dock, there are a couple of cute photo ops, such as a miniature Mayan pyramid, and a Mayan character that you can pose with. We probably spent only about an hour or two walking around this area before heading back to the ship. I didn't realize that there was a place to swim right there at the dock when we got off the ship, so we went back to the ship and spent the rest of the day at the adults pool
We are going back to Costa Maya on our Aug. 19th, 2006 cruise, and we'll probably do some kind of excursion. When we were in Cozumel we took the excursion to the Tulum ruins, but I'd still like to see the ruins at Chacchoben. From the pictures I've seen, it looks like a totally different setting than the ruins at Tulum. (ocean-front, not many trees compared to being in the jungle).
We also enjoyed walking around Costa Maya for that time because we didn't have the opportunity to walk around Cozumel much, because of the Tulum excursions. We would've had the time, but by the time we got back from the ruins, we were sweaty and tired and didn't want to walk around much.
Hope this info is helpful
