On Quinta Avenida there are lovely things in La Hacienda, Casa del Sol, Joyas de la Tierra, Selva y Mar, and Manos y Huellas. The beach in Playa del Carmen is a good place to meet people, especially around the Blue Parrot Hotel or Captain Tutix nightclub. Most of the chairs are rental only, and many of the women are topless. Almost everyone has an Indonesian sarong which doubles as a beach towel. If you decide to snorkel or swim far out, be sure to pick your head up every few minutes to watch for boats.
Boats do slow down near shore, but a tourist was run over and killed last Spring.
Xel Ha is much safer for snorkeling, but you can stay safe in Playa del Carmen just by picking your head up once in a while to see and be seen. Also, if the waves are high do not go out unless you are a strong swimmer because the undertow can surprise you. This advice seems like common sense, but the coast guard had to send patrols up and down the beach last Spring because people who couldn't swim were out in rough water trying to drown themselves. All in all the beach is still safer than the ones in Cancun - Playa del Carmen has fewer rip off artists and a weaker undertow. If you want something to show off on the beach, Screamink on 10th Street between 5th Avenue and 10th Avenue does tattoos and piercings.