On the deeper dives (90/100 feet) to the north of Playa and at Mama Vina (wreck mentioned in earlier post), the current tends to be strong. Just make sure your buoyancy is good and just fly along with the current. On other deep dives (60 feet and more), the current depends on the day. Sometimes you just cruise along and don't have to kick, other days you might need to be a little more active to see more of the reef. Some shallow reefs (max. 50 feet) like Barracuda and Sabalos generally tend to have stronger currents (Sabalos has stronger current than Barracuda) than other shallow reefs here. These two reefs are fun to dive and there's a lot to see.
As for down current, Playa's reef formations are very different from those of Cozumel (no drop offs like in Cozumel; also all dives conducted over sandy bottom) so you won't find what is like the underwater version of a rip current (that pulls you down instead of out). However, if you do end up diving in strong current, stay close to the reef where it will be less.
FYI the tarpon have started to arrive in Tortugas and will be here for the summer. Pretty impressive to see them in large schools at the north end of the reef.