With treats it is important to wean them off. You basically do this by, once the dog knows the command and performs every time, being more picky. So say you're teaching sit. The dog sits every time you say sit, you give a treat every time. Now what you would do is only give treats when the sit is as fast as you would like, stop giving treats for slow sits (still give verbal praise). If you desire for the sit to be in a certain position (facing you directly, not sideways or anything) start only giving treats for fast and correctly positioned sits, continue verbal praise for the others. So basically work your way down to the perfect sit in your mind. Then you can begin to completely wean them off of treats by only giving every once and a while throughout the session (make sure those times are never when the dog does sloppy sits) and eventually none at all. Make sure your verbal praise is still there.
As far as whether or not to use treats...I think they are great. I just think it is important that the dog see them as a reward and not a bribe (with some behaviors it is ok to use them as a bribe to begin but transition them to a reward as quickly as possible) and that they learn that the seeing the treat is not the only time they will get them, in fact they are more likely to get a treat when they don't see it (treats should be held out of the dog's sight when you give a command).
I also believe that treats are not always the most appropriate reward. For instance a dog that jumps up when he greets you really wants attention. The proper reward to train that dog not to jump will be attention, he will get it when he sits or behaves. For a dog that pulls on walks the proper reward would be walking, when he does not pull his walk continues, when he does it stops. For a puppy that nips the proper reward is usually play, he does not nip playing continues, he nips playing ends. Plus some dogs are more toy motivated than food motivated so using a small play session as a reward instead of a treat works great for them. SOME dogs even care enough about physical petting to be used as a good reward. I have not met any who will perform for simply verbal praise without being weaned from treats first or unless there is a painful/fear inducing/uncomfortable result if they do not obey. I'm not saying that certain dogs don't respond to it, I'm just saying I've never met any who do.
