The taxi system in Cancun is about as convenient as the bus system. Every second car on the road is a taxi, and you find groups of them parked around hotels and high-traffic areas.
One piece of advice you will always hear is: agree on the fare before you get in the cab. I followed this advice most times, forgot a couple of times, and it didn't seem to make much difference either way. But you should do it as a matter of course, in case you hit an unscrupulous driver whose only English is "200 pesos! 200 pesos!".
Fares to different parts of Cancun are posted outside the hotels. I found it difficult to get these exact fares as the taxi drivers would park a short way away from the hotel and would all quote the same fare that was $1-2 US more than was posted at the hotel. For comparison, here is the list of fares from the Omni hotel, in the middle of the hotel zone.
|From - To||Posted Fare||My Opinion|
|Omni - Plaza Kukulcan||17 pesos||overpriced|
|Omni - Plaza Flamingo||17 pesos||fair|
|Omni - Plaza Caracol||20 pesos||good deal|
|Omni - Airport||65 pesos||fair|
|Omni - Downtown||38 pesos||good deal|
|Omni - Playa del Carmen (Cozumel)||150 pesos||no idea|
I found the rates for the same trips in the opposite direction were a bit higher again. So, the best compromise between economy and convenience is to take a taxi out of the hotel zone (arriving quickly at your destination and getting a good price) and taking the bus back down the hotel zone (a leisurely, dirt-cheap ride).
I found the taxi approximately 5 times as fast as the bus. See the section on the bus system for a list of bus timings.
All the taxis are smaller cars than in the US. They are compact cars, often resembling Mazda 323s, where 3 in the back is a tight squeeze.