Updated December 2009
There are two competing ferry companies, UltraMar and Mexico Water Jets, that run from Playa del Carmen to Cozumel from the pier at the south end of town, they leave on the hour but not every hour so you should check the day before to see what time they run. Currently UltraMar's schedule for December 2009 is different for even and odd days of the month which seems kind of peculiar. The schedules I found on the internet are useless, they may change from day to day or month to month.
The ticket booths are right next door to each other as you approach the dock area, both in Playa and in Cozumel, the one with the next ferry will be the one that is currently selling tickets. There is no savings to buying a round trip so wait to purchase your return fare to see which ferry meets your schedule better, we bought a round trip and then had three hours to kill, fortunately they refunded our money from UltraMar and we bought tickets on Mexicana. They both take about 35-40 minutes and cost 140 pesos each way (currently $11 US). They only take cash but they take USD or pesos.
There was plenty of room on the ferry going both directions so you don't need advance reservations but get in line early if you want to sit in a particular spot.
Taxis are the easiest way to get wherever you can't walk in Coz. When you arrive at the airport, you will need to go to the little booth in the arrivals hall to pre-pay your fare to your hotel. It won't cost much since the airport is just a ten-minute drive from San Miguel.
For every other trip you make in a taxi, just flag a cab down in the street (it costs less than if you pick one up in front of a hotel), tell the driver where you are going, and he'll set the price, which works on a zone system.
A great way to see the island is to rent a scooter. Many sites on the net and guidebooks warn about driving on the island, but we had no problems at all. Parts of the westerncoast even have own lanes or roads just for bikes and motorcycles. The only problem we had was some confused dogs running around on the road, plus birds and bats coming a bit too close sometimes. But we never had any problems with the road, cars or other scooters.
There are plenty of places to rent scooters, so it's worth to check a bit around. Some have really great offers, but the price doesn't include anything. It's better to pay a bit more to get insurance, gas and other things included.
On a seven day cruise, we normally dock in 3-4 ports, one of which on this trip was Cozumel. Since Cozumel is an island just off the coast of Mexico, it makes for a great tour location for cruise ships. The pier is convienently located, and very easy to disembark from. Normally 2-4 ships are in port at all times, so it is a fairly hectic port!
Lots of people just rent scooters to get around the island. I must say that I was tempted, and might be tempted again.... However, lots of people, both locals and visitors, die in moped accidents on Coz. It looks like fun, but in fact you will probably get the crap scared out of you, even if you are an experienced biker.
If you want the independence of self-drive rather than using taxis, consider renting a car. Make sure you book ahead as demand often outpaces supply. Don't think you can rent a car in Cancun and take it over on the ferry--by all reports, it's fraught with frustration and difficulties.
If you stay near the downtown area, as I did, you only need your feet to get to most places. To go further afield, like going to the Mayan ruins or the east coast beaches, you will need wheels, though.
FYI so you get an idea of the walkable domain of San Miguel, enlarge the map in the photo. The place I stayed--Vila las Anclas--is shown with a blue checkmark.
If you are somewhere on the Mayan riviera you can take a ferry to Cozumel. The ferry goes from Playa del Carmen almost every hour. The ride takes about half an hour, and costs 10-15 USD for a roundtrip. The sea can be quite rough so if you have problems with seasickness it can be a good idea to take a pill before you go. If you are staying at Cozumel in your holiday you should take a day and go to Playa del Carmen or some of the other places on the Mayan riviera.
If you intend to travel around the island of Cozumel from the tourist center, renting a car is priceless! If you walk in to any budget rental care store front you can rent a jeep, suzuki, or VW safari (which was a blast) for the equivalent of 40 dollars a day. All of the sand beaches, Mayan ruins and the most beautiful remote parts of the island are pricey to get to by taxi so you end up saving money in the end. Also, it is impossible to get lost because there is only one road that goes around the driveable part of the island.
There are several ways of visiting Cozumel. I flew from Toronto twice, once direct and once changing planes in Cancun. The first flight we still touched down in Cancun, went through customs and got back on the plane. We were dropping Cancun passengers off that's why we had to stop there.
Another way is by ferry from Playa Del Carmen. It's a fairly cheap trip and many do day trips to and from the mainland this way. The ferry terminal is right in town in San Miguel, so once you get off the ferry, walk straight and the main square is in front of you.
You might also visit Cozumel on one of the many cruise ships that visit this port. It's quite a popular stop though the ships are damaging the reef since they've had to build newer docks for the ever expanding cruise ships.
To get around the island I would suggest renting a car unless you feel like renting a moped. A car is preferable to me as I was hauling my snorkelling gear with me, plus the top on the car was very handy since I once visited during the rainy season. I will say that my little VW Bug didn't have side windows so I still got wet. It was a convertible so I could take the top down if I wished.
It doesn't take long to circle the island so unless you plan on driving to and from your resort I wouldn't suggest getting a rental for more than a day or two because parking in town is a pain in the butt.
There's only one or two gas stations on the island, so watch the level in the tank.
You could do what I did to get a free car rental and that was to sit through a time share seminar. I was by myself and bored anyway, I knew I wasn't going to buy into it. But I did get a free lunch, a free blanket, free bottle of tequila and a day's car rental out of my time, so it was well worth it for me.
Pictured is my rental, very cheap car, the truck locked with a padlock, lol! But hey, it got me from point A to point B and that's all that mattered ;-)
Since Cozumel is an island, there are two ways to get there - by air and by boat. I took a little puddle jumper from Cancun. I got a free ticket on Delta to anywhere in North America by taking a voluntary bump. Almost all the flights (BWI to Atlanta to Cancun to Cozumel) were code-shares - most of them were not on Delta. When I went to get on the plane to Cozumel they had a fit and made me take the little open ended wrenches I had for my dive equipment out of my bag - no tools allowed. I had to leave them there - they gave them to the pilot to transport for me. I don't know what they thought I was going to do - take the plane apart bolt by bolt?
The pilot did take the wrenches to Cozumel for me and I retrieved them when I got there.
My husband flew directly in from Miami on AA. I don't think that flight is available anymore. He had an unused ticket from BWI to MIA, so all I had to do was get him a ticket from Miami to Cozumel.
The other alternative is to take a taxi or some land transportation from the Cancun airport to the ferry and then take the ferry over.
Cancun Airport....Playa del Carmen....Bus (operated by ADO or Riviera)...$8 per person one-way.
Cancun Airport....Playa del Carmen.....Colectivo (shared) taxi mini-van...$16 per person one-way.
Cancun Airport.....Playa del Carmen....Private taxi (3 or 4 people depending on luggage)...$50 upwards per taxi one-way.
Playa del Carmen.....Cozumel....Ferry (run by Ultramar or Waterjets)...$11 per person one-way.*
Or else come by cruise ship.