Jim,
A couple things about drift diving I didn't see mentioned here.
1) Typically the current is slower close to the wall/reef. If you are going too fast, just get closer and it will usually slow down. (Of course this requires good bouyancy control!)
2) Don't fight the current, go with it, unless there is something or some reason special to fight it. You will just use up your energy and air and shorten your dive.
3) I also found that the shallower reefs seemed to have worse current (in general). We did a "freeway dive" June 2003 that we called the "Grand Prix du Cozumel" because it was a ripping current. We started at Dahlila (sp?) and went past Francesca and Cedral.
4) On dives at Palancar (Caves, Gardens, Bricks or Horseshoe) the current has not been much of an issue. Out at the wall, over the abyss you can feel the current, but among the channels and caves and swimthroughs it was not bad at all. Santa Rosa and San Francisco were not bad either. (Of course swimthroughs and channels really force you to exercise and evaluate your bouyancy control. When you can do the up, down, over, under and around without thinking about it, with just breath control, then that is a very cool feeling, but I digress.)
5) When the current is running hard, the fish tend to hand under outcropping or behind coral heads downstream. You can do the same thing, and you will feel the difference in the current when you get behind "cover". Fish will eyeball you, but some will allow you to approach closer than normal because they really don't want to leave their protective shelter unless you really threaten them.
6) It can be a bit harder to explore all the nooks and crannies when you are drifting, but it is not always too bad. Just always try to stay upcurrent from the DM so that you can stop to see whatever they point out. It is quite frustrating to be just a little ways downcurrent from the DM and look back to see them pointing out things to the other divers, and see the other divers get all excited, but they are just a bit too far for you to fight your way back. Again staying closer to the reef will allow the others to drift ahead of you!
Just a few random thoughts. Hope they help.
Wristshot