I just had this article e-mailed to me, I found it facinating, albeit somewhat difficult to read, as it was written for a scientific journal.

I dont believe in using adversive training methods anyway, but after reading this, I'm doubly against "training" collars!

Karen Overall (2007), J of Vet Behavior
Considerations for shock and ‘training’ collars: Concerns from and for
the working dog community

http://www.dogdaysnw.com/doc/overall_collars.pdf