I too was told to go for the neck/head shot during the course... however, every bow hunter I know of that goes for turkey, (4-5) always shoots for the vitals (heart/lungs). The broad-side shot is very unlikely, given the movement you have to make to draw the bow, you'll want to wait, if possible, till they strut away from you, then draw back...
You can shoot them from behind, but i'm not sure of how much dmg is done to the meat when compared to a broad-side shot...
Personally, I've only managed to scare the hell out of turkey with the bow so-far...

but I'll keep trying... My in laws are getting pee pee that I refuse to take a SG out as they really want to try some... lol...
I've also heard reports of arrows bouncing off of the birds.. their feathers make quite a dampening effect on the arrows.... but I've never experienced it myself.