I've been spending time around really long throwers who mostly have no idea why or how it works, but it just does. For them I think it was all about in person training, as aDave was suggesting. The most common in person training we get is playing with better players, and I always noticed that being around long throwers and gauging their timing and form seems to be contagious, and I start to throw longer, too. For newer players reading the threads, this is a great justification for playing higher divisions than your rating would ordinarily suggest, or playing casual skins or doubles with pros who throw far...yeah, you probably won't win money, but you can consider your loss a tuition payment of sorts. I think the right kind of strength training is also important for those of us who aren't usually doing physical work with our hands (e.g., carpentry, painting, hanging drywall, auto mechanic, etc.). Of course we all know about the core, but hand and wrist strength is something that really needs conditioning to power through the right pec and get the most forward bounce.
Distance Drivers: Barsby Boatman, Glow Champion Katana
Fairway Drivers: Pinnacle Rival, Icon Patriot, Protege Rival, Elite-X Cyclone
Mid-Range: Ghost/Wasp, Z Buzzz/DGA Squall, Z Glide
Putt/Approach: Star Classic Roc, Icon Clutch, Protege Clutch