Taxis are a great way to get around Cancun. Visitors who want to explore Cancun Island, Cancun City and the areas south of town sometimes find it handy to rent a car for a day or two, but for the most part taxis do a great job of getting tourists around the island.
Finding a taxi is usually pretty easy in Cancun. Near most hotels, clubs and restaurants they usually park and wait for business.
Taxis are also usually available at Cancun International Airport, and at the ferry stops where the boats head over to Isla Mujeres.
Like most foriegn countries it's a good idea to get a verbal price from the taxi driver for the location you are going to before you get into the taxi. The taxi driver you ask has probably made the same run you are requesting many times before so he should have a pretty good idea of the cost right up front.
Many Cancun taxi drivers will quote you a price in pesos unless you ask them for a quote in US dollars. They may 'convert' your request from pesos to dollars with a slightly higher price on the dollar side, but if you keep the normal 10 to 1 pesos-to-dollars ratio in mind you won't get hurt too bad. Canadians can hang onto thier Loones as most taxi drivers will only accept pesos and US dollars.
Taxis are regulated by law as to how many passengers they can pick up, but these rules can be bent. Most vehicles are US-type sedans that can easily hold 4 passengers, and some can hold the maximum allowed by law which is 5 passengers. Taxi vans are a great way to shuffle larger groups of people around Cancun.
If you have questions about local destinations or points of interest Cancun taxi drivers are a great source of information. These guys live in town and are usually "in the loop" as to what is going on in and around the area. If this local knowledge is of interest to you be sure to pick a taxi driver that speaks decent English. Some do and some don't.
Tipping is not necessary for taxi drivers but providing a "propina" for excellent service or good local information is usually appreciated. Tipping more than 10% is not expected and not necessary.
To summarize taxis are a very practical way to get around Cancun. Keep in mind that many Cancun taxis drivers are willing to wait for you if you want to stop for a swim in the ocean, explore a certain beach, or just stop to enjoy the view!