Buton and AaronRiot and all the other Cozumel newbies out there reading these threads - I hope all this does not deter you from visiting Cozumel. It really is very rare to have these issues with downcurrents.
Fast currents at certain sites.... heck yeah, that is the norm. I have been to Paseo de Cedral over a dozen times and it can vary from good current moving at a reasonable pace, to blazing fast blur wild E-ticket ride. Ditto Punta Tunich... but both of those dive sites are favorites as the current brings in more fish and bigger fish. The wildest ride I had a Cedral was when we saw some huge nurse sharks, like every coral head had one under it ! And I always see turtles, HUGE angelfish, and nurse sharks at Punta Tunich.
There are ALSO plenty of dive sites with milder current due to location and reef structure. Most people go to Cozumel to enjoy the current and the ride, slow or fast, it always means great vis and tons of fish.
robin