According to my travel book, the beaches are very polluted as it is an industrial area. There has been much clean up done recently, but it is still "swim at your own risk," and the travel guide recommends pools.
They also have a section on "car robberies and bus hijackings are common--though on the decline" etc. It goes on to suggest that you not drive outside of the city proper, that you not drive between cities in the Acapulco area, etc. It suggests taxis around the city, and says that taxis from hotels cost 2-3 times what a taxi caught elsewhere will.
Absolutely NO personal experience here, just what the book says.