Fortunately, I've never witnessed any really harsh handling. However, training methods vary considerably and I can honestly say I have learnt things from every trainer I've come across.
The 'new school' methods practised by the two trainers I admire most seem to be based on a deep understanding of canine psychology and produce excellent results. Importantly, the training must match the age of the dog and the stage it's at. It can be really counter-productive, to try and teach a dog things it isn't ready to learn.
First and foremost, I've been trying to work on the basics of: Sit, Come, Wait, Heel. Get these right and I'll have an obedient dog.