Leslee, I took my dog Bixler (who had lots of behavioral problems when I adopted him) to the Petsmart classes. It was worth every dollar. Yes, I'm aware, as kwsm pointed out, that everything in that class can be found online or in a book. But I need structure! (For example, I have weights sitting around in my spare bedroom. But do I ever just go in there and lift weights? Hells no! I'm not self-motivated enough to do stuff like that!) Same for dog training -- having the scheduled classes and homework assignments kept me on task, and I probably wouldn't have been able to do that just self-teaching from a book or webpage.
Bixler had a problem being around other dogs (and he still does to some degree). The Petsmart class was great because he was forced to learn how to interact with other dogs in an appropriate (i.e. not "I'M GOING TO RIP YOU INTO A MILLION LITTLE PIECES) way.
The class taught him all the basic commands, plus a few neat tricks that I can show off to other people when they come over. And it gave me the opportunity to see how other people were working with their dogs, so maybe I could get better ideas about how to work with him. And although the trainers are not exactly "professional pet trainers" the one I had was definitely good enough to come up with many possible solutions to problems I was having.
So, I guess, if you are self-disciplined and can stick to a program and a schedule on your own, then you can get by with a book or an internet guide. But if you are like me and you need other people to get your ass in gear, then the Petsmart class is great.