Haipanda, I'm glad you are having a good experience with your training class. I think no matter if you learn any training at all the socialization for a puppy would be beneficial. Personally I don't think their staff are well trained and would not use them for "Training". I did adopt one of my dogs from a Petsmart store many years ago, but chose not to train with them.
My largest concern over your post would be a concern of the nutrition information they are giving you. If they are trying to sell you a product that they carry in their store I'd be cautious and make sure to do my homework thoroughly in searching out the info. They sell a lot of garbage dog food at Petsmart, and I'm certain that one of their objectives is to get you to buy it. I think if you search this website's food threads you'll learn a lot more valuable information on nutrition that you will from Petsmart. Just my
But please, don't take this wrong, good on you for doing what you are doing. Any and all training is beneficial.