I think the more class time you have the better off you are, but the skills you learn in class should be practiced on a regular basis.
The dive rescue course is great for rec divers to help there buddies, or others in the water. Personally I have never pulled a survivor out of the water, just bags. People have to realize that very few recover from a drowning. When my team gets called out to do a search, its only that. We go in for the recovery, or evidence search.
Its sad but theres an old saying," If we arent on scene when it happens and we have to put a tank on. Its probably too late." Also if a rescue is going to be made, its usually done by the first "glory hound(cop)" on scene, and usually the first one who rushes in becomes a victim as well.
-Greg